When is a slump not a slump? That's always one of the toughest things to figure out when considering the long baseball season. Is it just a bad month or bad tendencies finally catching up with a player?

In looking at the worst performers among hitters in the month of June, a few big names stuck out. For instance, Giancarlo Stanton barely sports a .700 OPS in the month, a dreadful number for a first-round talent. However, he has homered three times in the past two weeks and is clearly pulling out of his slide lately, so it's hard to be too worried about him at this point; the time to be worried was three weeks ago.

However, there are other Fantasy stalwarts who have struggled in June worth looking at. Here are five players struggling through a tough June who may soon force tough decisions on Fantasy owners:

Andrew McCutchen
PHI • CF • 22
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We're at an awkward point in Andrew McCutchen's career. He's not so old that we should expect a massive dropoff in his abilities, but not so young that it is out of the question. You don't necessarily expect players to fall off as hard as McCutchen has so far this season at 29, but he wouldn't be the first MVP-caliber Pirates outfielder to suffer that fate. And the biggest reason for concern might be that McCutchen is getting worse, not better, as the season has progressed.

After hovering around an .800 OPS in both April and May, the bottom has fallen out for McCutchen in June. His BABIP (.258) has cratered, but so has his ISO (.121), while his strikeout rate has spiked (28.3 percent) since the turn of the calendar. McCutchen has been one of the least productive batters in baseball in June, but his overall production this season tells the tale as well as any smaller slice.

To start with, McCutchen's plate discipline has slipped this season. He is swinging at 25.3 percent of pitches outside of the strike zone, per PITCHf/x, the highest rate of his career, and is making contact on just 49.4 percent of those pitches, by far the lowest rate of his career. McCutchen's swing rate and contact rate on pitches in the strike zone is just about where it was last season, so it really does seem like he is just having trouble identifying hittable pitches. And pitchers are challenging him more, which makes his struggles even harder to understand; 49.9 percent of the pitches thrown to him have been in the strike zone, compared to 47.6 percent last season.

McCutchen has also increased his fly-ball rate to 46.6 percent, well above career norms, which could be a sign that he is trying to make up for diminishing power by increasing his chances of putting one in the seats. Or it could be another sign that his swing is all messed up. Not every apparent change is conscious.

Whatever the answer, it's clear that McCutchen isn't right, and there aren't a ton of promising signs that make him a buy low. I can't say I would go out and trade for him right now, but I also wouldn't want to sell him at a discount on the chance he turns it around. You might be stuck.

Adrian Gonzalez
NYM • 1B • 23
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Like McCutchen, Adrian Gonzalez hovered around an .800 OPS in April and May before falling apart in June. But unlike McCutchen, his issues started last season. This might be more than a slump for Gonzalez, who posted an OPS of .701 or lower in three of the final four months last season, and had eight of his 28 homers in April. Over the past 365 days, Gonzalez has hit just .263/.340/.416 with 21 homers and 76 RBI in 154 games.

Gonzalez's fly-ball rate has dropped to 25 percent this season, by far a career low, and his hard-hit rate has similarly dropped to 31.5 percent -- not quite a career-low, but definitely within spitting distance. Hitting home runs requires a combination of a ball hit in the air and a ball hit hard, so if you're wondering why Gonzalez is on pace for just 12 in 150 games, there's your answer. At 34, age appears to have caught up with Gonzalez, and he is no longer a starting-caliber first-base option.

Nomar Mazara
DET • RF • 15
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Nomar Mazara doesn't have the name recognition or track record of the rest of this list, but he garnered as much excitement as any of them when he made his major-league debut and clubbed nine homers in his first 43 games. Given his age and status as one of the top prospects in baseball, it was easy to get excited about Mazara, and to project greatness to come.

So, it's fair to say June has been a disappointment. Mazara has still managed a decent .263 average, but the power he showed early on his disappeared, as his ISO fell to .101 in the month. He has just two homers in 26 games, and has continued to struggle against lefties. He sports just a .605 OPS and only two extra-base hits against them.

I identified Mazara as a candidate for homer regression in early June, and that's exactly what we've seen so far. His raw power isn't in doubt, and the fact that he leads baseball in average homer distance attests to that. However, Mazara's hard-hit rate has hovered around 25 percent all season, which makes it awfully hard to hit for consistent power. Mazara's future is bright, but his current lack of in-game power and platoon issues make him look like a fringe-starting outfielder.

Ryan Zimmerman
WAS • 1B • 11
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Zimmerman's struggles caused a panic in the beltway during May, as opposing pitchers opted to just not pitch to Bryce Harper, confident in the knowledge that Zimmerman wouldn't hurt them. Zimmerman actually did start hitting in May, with seven homers and 17 RBI, but he has been dreadful otherwise. He sported a .603 OPS in April and has somehow been even worse in June, hitting .171/.214/.289 in June with only five extra-base hits in 20 games.

Unlike Gonzalez, Zimmerman's overall hard-hit rate is actually up this season, to a very respectable 37.5 percent. That has translated to his second-best HR/FB ratio ever, so power really isn't the issue. The problem has been balls in play and strikeouts, and that's a trickier subject. Despite Zimmerman's healthy hard-hit rate, his line drive rate is down yet again this season, so it's no surprise his BABIP is down to .255. There might be room for positive regression there, but he was at .268 last season with a higher LD%, so there might not be too much hope for improvement. Combined with his career-high strikeout -- buoyed (dragged down?) by a career-high 9.9 percent whiff rate -- and we're probably looking at a player who will struggle to hit .250 moving forward. Does he provide enough power to make up for that? I'm not sure.

Alex Rodriguez
DH •
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This is what we expected Alex Rodriguez to look like last season, when he inexplicably clubbed 33 homers in his comeback tour. The soon-to-be 41-year-old has walked in just 4.8 percent of his plate appearances this season, while striking out 29.4 percent of the time, a horrible ratio. And he isn't doing much to make up for it as he slogs through the year.

Rodriguez actually has a healthy 18.2 percent HR/FB ratio, but has nearly doubled his infield fly-ball rate from last year, while his hard-hit average has predictably slipped. He has just a .564 OPS against right-handed pitchers, and the Yankees may just use him as a platoon option at DH moving forward. As a DH-only player in Fantasy, the bar for Fantasy relevance is even higher for Rodriguez, and he isn't coming close to that. There just aren't many signs to look at for optimism right now, and he probably doesn't deserve to be owned in any Fantasy formats at this point.