Who can't top what they did in 2013?

You might think sabermetrics is merely the pursuit of joyless predictability, but a big part of my enjoyment of sabermetrics doesn’t come from the results that match our expectations but rather is derived from the guys who totally upset them, guys whose results defied prediction or anticipation. The trick is that most of them can’t sustain that kind of surprise. The 2013 season gave us our fair share of guys who broke out, but here’s a group of five who will have a hard time topping what they did last season, not just in 2014, but ever.

Let’s start with third baseman Josh Donaldson of the Athletics. Starting off as a hot-corner conversion project to help the A’s paper over their lack of a viable alternative, the former catcher busted out big, ripping 64 extra-base hits and finishing fourth in the AL MVP race. He put up an 8.0 WAR season, good for fourth in the major leagues, a better year in that regard than the ones put up by Miguel Cabrera and Robinson Cano. Donaldson’s .883 OPS wasn’t just unexpected, it was totally out of character from everything we’d already seen from him, 50 points higher than his minor league career rate. His walk rate also significantly outperformed his minor league numbers, and his .333 BABIP was significantly better than anything he’d done in any full season in the minors.

If you can set aside any reservations you have about WAR, eight-win players don’t just manifest out of thin air. Among the 115 guys who’ve had eight-WAR seasons since the start of the divisional play, the only guy who might be more surprising to see there than Donaldson was Bernard Gilkey and his big year back in 1996.

So, where did that Donaldson leap come from? Was it the benefit of finally not having to deal with the wear and tear of catching? Or perhaps a classic case of a guy busting out in his age-27 season? A mere BABIP aberration? Whatever it was, that was followed by some postseason shaming at the hands of the Tigers, creating questions. However, that’s the best rotation in the league, and Donaldson didn’t face especially weak competition (ranking 53rd out of 107 AL batters with 400 or more plate appearances according to Baseball Prospectus), so it wasn’t merely a matter of clobbering weak opponents.

As fun as it was, it’s hard to see Donaldson sticking around at this level of production consistently, if only because it would be unprecedented. The Bill James Handbook forecast a 77-point tumble in OPS, and other projection systems are going to be similarly predictably skeptical, anticipating a drop-off because that’s how they generally work with players with histories like Donaldson’s. On the half-full side of the glass, though, if you had told A’s fans a year ago that they could have a third baseman who could put up a .780-.800 OPS with good D and durability, they’d have offered you their firstborn in exchange. It might all be downhill from his 2013, but Donaldson should remain an asset for a contender. Not many guys can shed 100 points of OPS and still say that.

Moving over to pitchers, one easy exercise in separating actual performance from what you were supposed to get given a pitcher’s peripheral numbers such as strikeout and walk rates is to subtract a guy’s ERA from FIP: Presto, you have a leaderboard of surprise pitchers you might want to bet against. I’ll start with Hector Santiago because he’s someone who just got dealt and the Angels are banking on, but he’s also someone who’s likely to see his ERA jump by a run if FIP is any guide.

As promising as Santiago’s arm is because he’s a southpaw with low-90s heat, a big part of the problem is the huge number of people he’s putting on base. Only Jake Arrieta and Jason Marquis put more people on first base via unintentional walks and hit batsmen than Santiago’s 13 percent clip last season. The hit batsmen -- 15 last season alone -- might partially be a function of Santiago’s need to work inside, which he had to do to survive pitching at U.S. Cellular Field, the best home run ballpark for right-handed hitters; as HotZone reflects, he struggled when he let righties get good extension. Getting out of the Cell should spare him many of the penalties of making a mistake in the zone, but, if his command isn’t just a function of that environment -- and he was still putting guys on first base at a 12 percent clip on the road last season-- you probably can expect his ERA to go up as much as FIP suggests.

Joe Kelly of the Cardinals is another name in that ranking of pitchers to worry about who might surprise you after the role he played in their pursuit of the National League pennant, posting a 10-5 record and 2.69 ERA. Add in a fastball that sits around 95 mph and what’s not to love? Approached analytically, the problem is the absence of strikeouts, where FIP “expects” more whiffs. In the real world, Kelly works hard at being an effective sinker/slider guy as a starter, pounding the bottom of the zone, which produces an exceptionally poor strikeout rate (4.8 K/9). That plus a lot of run support (almost six runs per nine last season) produced the contrast between the gaudy win total and ERA against a 3.98 FIP and the expectation that run support comes and goes. What you’re left with is a guy who still looks pretty good if you’re talking about your team’s fifth starter, his lot with the Cardinals, but if you were banking on big win totals and an ERA under 3.0 in a full season of rotation work -- don’t.

Because I set my cutoff at 70 innings, Rangers reliever Tanner Scheppers is easy to pick on because of the distance between his expected and actual performance: A 3.77 FIP versus his 1.88 ERA. There’s a pen man like that any given season; it’s always harder to sustain that kind of fluky discrepancy over a larger number of innings. But, as a sinker-slider guy, Scheppers is a defense-dependent ground-pounder, which is why he profited greatly from inducing an MLB-best DP rate of 24.5 percent in double-play situations. If he can continue that kind of execution, that’s great, but can you bank on it? Even a slip back to something closer to league average will mean a bunch of runs allowed in tight late-game situations for the Rangers, as well as a big jump in Scheppers’ ERA.

Finally, let’s talk about outfielder Marlon Byrd. A 30-something slugger who owes a big chunk of his power production to Texas’ home park leaves after 2009, has two disappointing seasons with the Cubs, then falls over a cliff in his age-34 season. And that’s it for him, right? Not at all: Byrd’s big bounce-back in 2013 after earning a job with the Mets in spring training made him a key stretch pickup for the Pirates. His combined .511 slugging percentage made him this winter’s quick addition to the fast-acting Phillies for two years (or three if a 2016 option vests) at $8 million per annum.

There are all sorts of “that won’t be easy” warning signs about Byrd’s 2013. Can he repeat a career-high .220 Isolated Power clip as a 36-year-old? Or a .353 batting average on balls in play, his best mark since his breakthrough 2007 season with the Rangers? Or a career-best 11.1 percent clip of homers on fly balls? It’s notable that Byrd has become a significantly different, more aggressive batsman with age, striking out a career-high 24.9 percent of the time last season while his unintentional walk rate plummeted to 5 percent, while also becoming a more pronounced fly-ball hitter.

That would be a tough act to sustain for people with considerably stronger track records than Byrd’s. Tip your cap to Byrd for earning another multiyear deal in his 30s, but don’t be surprised when this turns out as badly for the Phillies as it did for the Cubs.

Christina Kahrl covers baseball for ESPN.com. You can follow her on Twitter.