Half the fun of the early stages of any sports season is the rampant participation in "Overreaction Theater" -- the tendency to put too much stock into a very limited early sample size. 

This is particularly egregious in baseball, as many players either start off slow or come out of the gate scorching-hot. Trevor Story has 7 home runs in 28 at-bats, while Troy Tulowitzki has just three hits in his first 28 trips to the plate. I'm certainly not betting that Story will have a better season than Tulo, but here we are:

While nearly everyone regresses to the mean (either forwards or backwards), it's important to find the players who are capable of sustaining their early success. Here I'll look at five under-the-radar pitchers who may have the stuff to turn their hot starts into an above-average fantasy season.

1. Jeremy Hellickson (SP, Philadelphia Phillies)

Jeremy Hellickson was once one of the top pitching prospects in baseball, but he never quite panned out for the Rays despite some flashes of brilliance here and there. The stuff has always been there, as he backs up an average fastball with a superior changeup and decent curveball. His control is typically excellent, and while he isn't the strikeout machine many thought he'd be, he has the potential for a post-hype breakout. He's started off 2016 with a 1.54 ERA and 0.60 WHIP across 11.2 innings, and while he won't maintain anything close to either of those numbers, he could still be the de facto ace of the rebuilding Phillies.

The diminished velocity on his fastball is going to force Hellickson to pitch smarter. He topped out at 95 in 2010 during his first taste of the big leagues, while he hasn't yet dialed it up past 90 this season. It's of course very early in the season, but I expect Hellickson to hover around 91-92 on his fastball as he did last year, which certainly isn't enough to blow past big league hitters. His success will come from pitching like Dallas Keuchel-pinpoint control and effective use of his changeup to keep the ball on the ground. Hellickson's 13.3% home-run-to-fly-ball rate (HR/FB) from last year will most definitely come down, and with any sort of luck in the BABIP department, Hellickson should be able to keep his ERA below 3.75. 

2. Colby Lewis (SP, Texas Rangers)

Remember how Colby Lewis won 17 games for the Rangers last year? Me either. 

The veteran hung around in enough games to pick up the highest win total of his career, partially a product of his highest innings pitched total (204.2) since 2011. That win total was a borderline miracle, because it came with an ugly 4.66 ERA and 4.62 xFIP. 

Lewis was exceptionally lucky in a couple of ways -- his .267 BABIP was well below his career average of .300, and his 8.9% HR/FB rate was also much lower than the league average (and his career average). Lewis did demonstrate some of the best control of his career though, as the 1.85 walks per 9 innings (BB/9) was the lowest he's ever posted in a full major league season. 

The room for regression to the mean says everything. I don't see how Lewis comes anywhere close to last year's win total if the stats above approach his career averages, and given that he'll turn 37 this year, there's absolutely no reason to expect him to make any strides forward elsewhere. His 3.00 ERA and first two quality starts will not be the norm in 2016, and I'm passing on him moving forward.

3. Jimmy Nelson (SP, Milwaukee Brewers)

Nelson started 30 games for the Brew Crew in 2015 and didn't do much to indicate he could ever be more than a third or fourth starter. The biggest issue for the powerful righty at every level has been control -- he had 3.30 BB/9 in 2015, and he'll need to improve on that number to take a step forward in 2016. His bread-and-butter is a sinking fastball that sits around 95, and if he can start to spot that and his out-pitch (slider), then he can be very effective both as a ground ball and strikeout pitcher. 

Nelson is still early enough in his career to make adjustments. He's started off 2016 on the right foot, allowing just four total runs across 13.1 innings. His most recent start (April 10th against Houston) was a microcosm of his potential and problems -- six innings of two-run, nine-strikeout ball with four walks and two homers against. While the win total likely won't be there on a very bad Brewers team, his strikeout totals and ratios should yield plenty of success over the season... if he can keep that sinker down.

4. Aaron Sanchez (SP, Toronto Blue Jays)

The term "electric" is thrown around a lot, but for Sanchez, it just fits. His fastball reaches 95 mph and has an absurd amount of movement when he's really in the zone and generates a ton of looking strikes. He backs it up with a sharp curveball that dives in an instant, and when both pitches are on, he's nigh untouchable. At just 23, Sanchez is still in the development stage. He threw well enough in spring training to crack the Jays' Opening Day rotation and has been their most impressive starter through two starts. He's allowed just two unearned runs in 13 innings (both a result of solo shots) and has averaged a strikeout per inning.

It's easy to tell Sanchez has the stuff to be a big-league ace when you watch him pitch, it will just be a matter of him honing his control. As is often the case with young power arms, it can take a while to master the control of their most devastating pitches. Sanchez has a 4.27 BB/9 rate over his professional career, and he did have three walks in his most recent start against the Yankees. I like his chances at putting up a sub-4.00 ERA this year, but we may still be a year away from a true breakout. 

5. Edinson Volquez (SP, Kansas City Royals)

Volquez has bounced around quite a bit during his 11-year career, but the last two have been his most successful. Volquez was excellent in Pittsburgh in 2014, posting a 3.04 ERA (although his 4.20 xFIP indicates he didn't pitch quite as well as the numbers imply), and he backed it up with a 3.55 ERA (4.26 xFIP) in 2015 for the Royals. A large part of his success was due to keeping the ball in the yard, as he averaged 0.755 home runs per 9 innings in those two seasons. As is the case for many veterans his strikeouts per nine dropped off, forcing him to rely on his sinker and a newly-developed knuckle-curve to pitch to contact. 

The xFIP makes me very nervous. While not a flawless stat, it does negate some of the luckier aspects of pitching like defense and sequencing, and it indicates Volquez isn't actually pitching as well as his final stat line shows. In his age-33 season, he's not yet at the point where I'd consider him a risk for age-related decline, but I also don't see him improving in any way. Volquez's ERA should be closer to 4.00 this year. And while he'll still rack up 12-plus wins, the numbers don't indicate any him being exceptional in any way.  He had 10 strikeouts in just 5.2 innings against the Twins in his most recent start, but that should be a vast outlier for this crafty veteran.