Quite a few rookies generated strong exit velocity readings in various sample sizes last year. Exit velocity is an important measure for a hitter because the harder a ball is hit off the bat, the more likely strong offensive production occurs. This graphic, from Daren Willman of baseballsavant.com and now of MLBAM:
As the picture shows, most home runs occur on batted balls hit over 100 mph, and only 13 batted balls that left the bat under 90 mph went for home runs all year. Batting average also significantly rises as exit velocity rises into the mid 90s. On average, hitters will bat over .400 on balls hit 95+ mph, while approaching .700 for balls hit 105+ mph.
According to statcast, MLB average exit velocity was about 89 mph in 2015. These five 2016 second year hitters had average exit velocities significantly above MLB average last year:
Kyle Schwarber, Cubs (94.3 mph average exit velocity)
I had the chance to see Schwarber in person a few times this year and one observation that stuck out to me was how light he made the bat look during his warm up cuts. The effortless bat speed was ridiculous, it looked like he was swinging a whiffle ball bat. Something else that jumped out at me was his home run off Jacob deGrom in game 3 of the NLCS; Schwarber took a less than full swing at a 97 mph fastball located a foot outside and flicked it opposite field for a home run. The wind was blowing out a little at Wrigley, but it was still amazing. Schwarber is a monster hitter in the making, and his 16 HR in 273 PA last year is a sign of things to come.
Michael Conforto, Mets (93.3 mph average exit velocity)
In the regular season, Conforto hit to a 134 wRC+, .841 OPS, and .236 ISO with 9 HR in 194 PA, mostly against RHP. Conforto flashed his potential in the playoffs, with a 113.5 mph laser home run off Dodgers ace Zack Greinke in the NLDS and a two home run game in the World Series (one of which was off a LHP). I absolutely love his swing and approach at the plate, and I think he will emerge as a star hitter maybe as soon as this upcoming year.
Joc Pederson, Dodgers (93.1 average exit velocity)
Pederson was horrible in the second half, but the overall package at the end of the year was still pretty good. He hit to a 115 wRC+, .763 OPS and .206 ISO with 26 HR in 585 PA. The second half drop in production is concerning, though, and it wasn't just baseball randomness; his average exit velocity dropped to 89 mph after July 1, a significant decline from where it had been prior to July 1. There's a fair chance the drop in production was a result of the league adjusting to him and exploiting weaknesses, and if that's the case, it'll be up to Pederson to re-adjust next year. There is a lot of talent in the bat, though, and a few tweaks can put him right back on track. Pederson's main value will come in OBP leagues, where his double digit walk rate vastly makes up for his rancid batting average.
Greg Bird, Yankees (94.5 mph average exit velocity)
Bird was called up to fill in for the injured Mark Teixeira at 1B in August and hit to a 137 wRC+, .871 OPS and .268 ISO with 11 home runs in 178 PA. Currently, Bird has no spot on the big league club and will start the year in the minors, but is just a Teixeira injury away from manning the 1B position. With Teixeira's tendency to get banged up, Bird will be on the fantasy radar all season.
Miguel Sano, Twins (94.9 mph average exit velocity)
Using 140 BIP as the qualifier, Sano's 94.9 mph avg exit velo was third highest behind only Giancarlo Stanton (99.1 mph) and Miguel Cabrera (95.1 mph). Sano hit 18 HR in 335 PA, with a 151 wRC+, .916 OPS and .262 ISO, and his walk rate of nearly 16% was 6th best in the game (300 PA minimum). He does have some swing and miss in his game, though: his 35.5% K% was highest in baseball, and his 60.9% contact% was lowest. Sano features arguably the best raw power in the American League and will be a consistent 30+ home run threat yearly.