Week 16 of the NFL season opens on Saturday afternoon at 4:30 p.m. ET with an AFC battle between the Baltimore Ravens and Indianapolis Colts. The Ravens are 13.5-point favorites, up from opening at -12.5. The Over-Under, or total number of points Vegas thinks will be scored, is 41, unchanged from the opening number.

With so much at stake and the line on the move, you need to hear what SportsLine's Mike Tierney has to say.

A veteran sportswriter with decades of experience covering the NFL, Tierney studies matchups like nobody else, and he's used his expertise to crush NFL picks. After yet another cash on last Saturday's Chiefs-Chargers game, he's now an insane 48-22 on those selections since the start of last season. Anybody following his picks is way, way up.

Now, Tierney has analyzed every matchup, every trend, and every angle for Ravens-Colts and locked in his Over-Under pick.

Tierney knows the Over might not get much help from Indianapolis. The Colts are second-to-last in the NFL in points scored per game (16.1) and haven't scored more than 20 points in a game since October. They've averaged just 10 points in their last three outings.

And it won't be any easier against a top-tier Baltimore defense. The Ravens are fourth in the NFL in scoring defense (18.3 ppg) and have given up 20 points or fewer in four of their last five games. Their only defensive setback during that span was a 39-point outburst by the the Steelers.

But just because this is a stingy defense going against a struggling offense doesn't mean this game will go Under, especially with a low total of 41.

While the Colts can't be counted on to put more than 20 points on the board, the Ravens' offense, which struggled earlier in the season, has become significantly more potent in recent weeks.

Baltimore has scored at least 23 points five consecutive weeks. And the last time the Ravens played a defense as poor as the Colts', they exploded for 44 points against the Lions -- a team ranked 27th in the league. The Colts come into Saturday's game ranked 30th. 

And SportsLine's advanced projection model is calling for a big day from Ravens QB Joe Flacco. It's predicting over 250 yards and two touchdowns for the Baltimore signal caller, with WR Mike Wallace being the best bet to find the end zone receiving.

Ravens WR Jeremy Maclin is doubtful for Saturday's game with a knee injury, so look for more involvement from Wallace and tight end Benjamin Watson. Maclin will go against a Colts' defense that will be without its top corner, Rashaan Melvin.

On the ground, the model is calling for well over 100 yards rushing for Ravens running backs, led by Alex Collins, who had 120 yards and a score two weeks ago against the Steelers.

Tierney has evaluated all of these angles and while he's leaning on the Colts to cover the spread, he knows there's a huge x-factor that ultimately determines whether Colts-Ravens goes Over or Under. And he's sharing it over at SportsLine.

So which side of the total should you back in Ravens-Colts on Saturday? Visit SportsLine now to see what big x-factor sends Ravens-Colts Over or Under, all from the expert cashing on almost 70 percent of his NFL totals picks since the start of last season.