When this season started, the Boston Celtics were a popular pick to represent the Eastern Conference in the NBA Finals. Now, it's the Milwaukee Bucks who hold that distinction. After both swept their first-round series, Boston and Milwaukee will square off with a trip to the conference finals on the line, and what a series it should be. Game 1 is scheduled for Sunday at 1 p.m. ET. Below are some quick thoughts on things to watch for in this series. 

Giannis Antetokounmpo vs. Kyrie Irving

Obviously both these guys will have a disproportionately huge say in how this series goes. "Nobody can guard either of them one-on-one," a scout told CBS Sports, but the key will be how each respective team TRIES to guard the opposing star. 

You're going to start hearing the name Semi Ojeleye a lot. A little-used Boston bench player who's built like a brick house, Ojeleye has had some relative success -- and I stress the word relative -- defending Antetokounmpo, or at least mildly interrupting his Euro-stepping quest to destroy the NBA and perhaps the entire earth in the process. Brad Stevens was asked if Ojeleye could see some expanded playing time in this series. "He could," Stevens told reporters, so there you go. 

Whether Ojeleye sees minutes or not (and I suspect he will, at least early, until Stevens can see how much it hurts the offense), this is going to be defense by committee on Antetokounmpo. The good news is the Celtics have multiple bodies for the job -- Marcus Morris, Jaylen Brown, Jayson Tatum and Gordon Hayward will all see time, more than one of them on a lot of possessions as the Celtics will switch a lot of stuff, and in transition it'll simply be the closest body picking Antetokounmpo up before he becomes a runaway train. 

As for "how" the Celtics will attempt to slow down Antetokounmpo -- whether they'll give him a big cushion or try to close some of his space on the ball -- that's a matter of more interesting discussion. Perhaps the most important thing is not how they guard him on the ball, but how they choose to deploy their help defense, and how well the help defenders execute those split-second decisions in the heat of the moment. We'll get to that in a bit. 

As for Irving, he presents his own kind of problems. Eric Bledsoe will likely see most of the time on him, along with George Hill, and Irving won't be stopped by either one. He was terrific vs. Indiana in the first round, finding an almost perfect balance between his own aggression as a scorer and making sure other guys get into their rhythm. Irving will have to walk that line again, but the Celtics need him to score big in this series, no question. He should have a great opportunity to get loose in the pick and roll/pick and pop with Al Horford, which we'll also get to in a second as we talk about the biggest defensive decisions each team has in front of them.

Bottom line, whichever star is better in this series is going to give his team an upper hand. Kyrie is fantastic, but Giannis has been the better player this season, and the decisions he forces the defense to make are unending with all the shooters around him, whereas Kyrie is a bit more of a conventional cover. Plus, defensively, Giannis can ruin a lot of what Boston is going to try to do, while Kyrie is going to be spotlighted time and again in isolation/postup plays, and his simply holding his own in those situations will be the best Boston can hope for. 

The big thing here is Kyrie's knack for the big stage. We saw what Damian Lillard just did to the Thunder. We've seen Kyrie be absolutely brilliant deep in the playoffs. This is such a close call between the stars. But at the end of the day, Giannis is the most unstoppable force in the world right now. Well, maybe outside of Damian Lillard. 


Defensive decisions

Giannis puts defenses in a couple different pickles. First, do you sag off him because he can't shoot or crowd his space so as to not give him a runway to get a head of steam and do things like this?

Notice how open the lane is there. That's because Milwaukee, almost exclusively, plays four capable 3-point shooters around Giannis, which pulls all the defenders onto the perimeter, which creates the second question: Do you stay attached to the shooters and let Giannis go one-on-one with no rim protection behind the on-ball defender, in which case he'll most likely do something like he did in the above clip, or do you help down off the shooters to keep Giannis from dunking 50 times a game, in which case he does something like this?

The question of when to help and when not to help is central to modern NBA defense, and never is it more in a spotlight than when going against Giannis and the Bucks, who basically make you make that decision every single possession. 

"If it's a penetrating drive, meaning the driver is going to get to the restricted circle, you might have to help. A few shooters you still might not leave in that situation, but basically, if [the driver is] getting to the restricted circle you should come off and help down," Pelicans assistant coach Darren Erman told CBS Sports early in the regular season. "If it's just a flat drive, where the driver is only getting to the paint but not the restricted circle, then you stay out with shooters. 

"Klay Thompson was really adamant about this when I was with Golden State," Erman continued. "One day he said to me, we were talking about a play where somebody was driving in him, and somebody over-helped and gave up a 3-pointer on the kick-out, and Klay said, 'We have to understand, I had that guy covered. He wasn't going to score on me.' 

"So you work on that, but it's a really hard line to walk, and you have to make that decision in a split second. You know 3-pointers kill you, but if a guy is living in the paint all game that's even worse. That just puts so much stress on your defense and you eventually buckle. So one way or another you have to control dribble penetration. If you don't have perimeter defenders who are good at that, or you're playing against a guy like, say, a James Harden or Giannis where you can't expect even a good defender to stay in front of them, then you probably error toward help. But then it becomes about where you are on the court and what shooter you're leaving. 

"So all these little decisions [come] in a split second. If you're above the break, maybe you help down to the nail and then recover back out. Strong side corner, stay attached. Weak-side shooter, maybe you don't shade down as much as you used to, because the reversals are so fast now. It's all about decisions and discipline. Any little crack in the chain makes for one pass and an open shot."

Got all that? It's a lot, obviously, and it happens fast, and how the Celtics respond to this decision over and over again will be such a big part of this series. You can have principles, film study, coaches in your ear, whatever you want, but at this point of the playoffs in this close of a matchup, the stakes of each and every possession go up exponentially. As such, the possibility of getting a little jumpy and overreacting is always lingering. Staying disciplined while playing on the edge of your seat is not easy. That's not an X's and O's thing. That's a human nature thing. 

The Bucks, of course, have to make all these same decisions when they're on defense. The Celtics don't have a straight-line driver like Giannis, but they have a ton of guys who can put the ball on the floor and get to the cup and a ton of shooters, too. So roughly the same dilemma exists. That said, the Bucks are very clear on their priorities here: They're going to guard the paint and the rim first, and if that means over-helping and dropping their bigs into the paint and giving up a bunch of 3s as a result, so be it. 

"We're not happy to give up that many 3s and we're not willing to, it's just, there's things we do really well -- protect the paint, rebound, I think our activity is a positive -- but if we could reduce the number of 3s, we'd love to," Mike Budenholzer told CBS Sports late in the regular season. "We're not in any way, shape or form happy about [giving up so many 3s], but we are overall pleased with where we are defensively [going into the playoffs]. You just have kind of understand that if we're taking care of the paint, we're taking care of the boards, we're being really active, we're really competitive, then those things are outweighing the negatives of giving up 3s."

The strategy, to Budenholzer's point, worked in the regular season. The Bucks gave up more 3-point attempts and makes than any team in the league this season, yet still they had the No. 1 defensive rating in the NBA. It also worked just fine in the first round too, but that was against a wildly inferior Pistons team and you can't really draw much from that. Question is: Can this work against Boston? The Celtics have a ton of shooters, and the Bucks are going to give them shots, and through the old "puncher's chance" prism, if a few of them get hot, you can see the problem for Milwaukee. 

Brook Lopez is central to this. One of the main reasons Milwaukee drops deep into the paint with Lopez is he can't guard on the perimeter. He'll get cooked. So they play to his strength, guarding at the rim alongside Giannis, making for a forest in the middle with plenty of light around the edges. Watch Lopez (No. 11) in these following clips and pay attention to how he's always moving into the paint at the expense of leaving a shooter:

This is one reason a lot of people think Brad Stevens will deploy mostly small lineups with Horford at the five. If Aron Baynes is on the court, it gives Lopez a natural big to cover who's not going to pull him out to the perimeter. When he has to guard Horford, he'll be put in a ton of two-man actions with Horford and Irving. If the Celtics get Lopez switched onto Irving, forget about it. He's done. But what will happen more often is Lopez will do his normal retreating into the paint and Horford will pop for either a wide-open look or a quick swing to a shooter.

If the Celtics prove too productive in these sets, would the Bucks have to consider benching Lopez for stretches to match Boston's smaller lineups? That's drastic, and I don't foresee much of it, but that's the chess game. Lopez is vital to what the Bucks do on the offensive end with his ability to shoot from deep and pull centers away from the rim for Giannis' drives, and if they have to take him out, or adjust the way he's comfortable playing in any way, that's a big win for Boston. 

So, who has the defensive edge? This is another close call. It's basically the Giannis factor and how impossible he is to cover vs. all the 3s the Bucks give up. I think the surrendered 3s are going to be a big problem for Milwaukee, and Boston is really in a groove defensively. Boston, theoretically, can load up on Giannis and build a wall in the paint, but you can't cover every Boston shooter with four defenders (accounting for Lopez staying in the paint). Boston is going to get a ton of open looks in this series, which is the main reason why our data engineer, Stephen Oh, who has run 10,000 simulations on this series, sees a ton of value on the Celtics winning. We'll get to that shortly. 


3-point shooting

Both team have a ton of shooters. For Milwaukee, Lopez, Bledsoe, Khris Middleton, Nikola Mirotic and Malcolm Brogdon all made 100-plus 3-pointers this season, and Tony SnellErsan IlyasovaSterling BrownPat Connaughton and even George Hill have to be respected behind the arc. Brogdon being out hurts. He shot the 3-pointer at better than 42 percent this season on over three attempts per game. 

For Boston, five players made over 100 3-pointers, and Brown, Hayward and Horford made 95, 77 and 73. The X-factor here is Hayward. He looked a lot more like himself down the stretch of the season, and in Game 4 against the Pacers he looked pretty darn close to all the way back. He was explosive with his first step and going to the rim and finished with burst, and when that put defenders on their heels, he stepped into 3s with confidence and nailed all three of his attempts. That extra shooter and play-maker for Milwaukee to account for could be a swing factor. 

Bottom line here, Milwaukee survives on a lot of good-but-not-great shooters adding up to a deadly team, but individually, when they get it going, the Celtics have some more top-end shooting firepower. The Bucks made more -- 13.5 per game -- than any team in the league outside of Houston this season, but again, they also gave up the most (13.1). Boston was right there with the Bucks, making 12.6, which ranked sixth in the league, but the difference is they gave up almost two fewer 3s per game than Milwaukee. 

This is all a very statistical, nerdy way of saying both these teams have a bunch of good shooters and offenses geared toward letting those shooters shoot. The team that makes more will have the advantage in the series, simple as that. I don't think there's any way to tell which team that will be. This is the ol' "make or miss league" adage come to life. 

ADVANTAGE: Too close to call


The Bucks can go nine to 10 deep even without Brogdon. The Celtics, without Marcus Smart, really only go eight. That could be nine if Ojeleye, as mentioned earlier, enters the regular rotation. But who knows how much time Baynes will see here. While the Bucks have more bodies, the Celtics have top-end bench talent. Perhaps Hayward or Morris enters the starting lineup in place of Baynes, but in looking at the starting lineup Boston deployed against Indiana, Terry Rozier, Morris and Hayward were coming off the bench. They accounted for 49 points in Game 4 to close out the Pacers. Every one of those guys is a starting-caliber player. If Smart (torn oblique) makes it back by the middle of the series, you either add him to the bench or Brown goes back there. That bench is thick. 

For the season, Boston's bench averaged 39.3 points, good enough for ninth in the league. Milwaukee was 26th with 31.8 bench points, and that's even with them blowing a lot of teams out and the bench getting a lot of garbage time at the end of games. When and if Brogdon comes back, Milwaukee's bench will deepen and strengthen, but for now, Boston can beat you with so many different guys who can pay so many different positions, giving Stevens the ultimate lineup versatility. 


At +240 in Vegas, can the Celtics win the series?

Of course they can win the series. I have Milwaukee winning in seven because I think, in the end, they have the most dominant player, and everything else is very close. But at that kind of value? As mentioned above, our resident data engineer ran 10,000 simulations for this series and concluded "it's a coin-slip series." In Stephen's model, he can tell which data points result in the biggest result swings, and for this series the number of 3s Milwaukee gives up really hurts in the sims. 

Personally, I agree with the data here. I picked the Bucks to win by a smidge, but at almost 2.5 to 1, that's a bet worth taking a shot on. Remember, the Celtics were the clear favorite to win the East to start the season, and there is reason to believe with the return of the real Gordon Hayward and the grit and chemistry they showed vs. Indiana, that team has arrived. 

VALUE BET: Celtics