How Will the Top Rookie MLB Position Players From Last Season Perform in 2015?

Kevin Kiermaier, Tampa Bay Rays, OF

Kiermaier, whose 4.0 fWAR was second among rookies and 3.7 rWAR tied for third, was a quietly valuable player last year for the Rays. Most of his value came from his glove and ability to hit for power, as he slashed .263/.315/.450 with 10 home runs in 364 plate appearances.

The 24-year-old excelled in the field, ranking seventh among big league outfielders with a 17.7 UZR. His 36.3 UZR/150 was second behind only Kansas City’s Jarrod Dyson among outfielders with at least 400 innings played, according to FanGraphs. He split his time between right and center field last year but is expected to be Tampa Bay’s full time center fielder in 2015.

While his defense may not have been that surprising, his ability to hit for power certainly was. In 1,724 plate appearances in five years in the minor leagues, Kiermaier posted a .398 slugging percentage and a .119 ISO, while hitting 15 home runs.

In one season against big league pitching, he almost matched this home run total and his .187 ISO shattered his minor league average. This was curious, not only in light of his minor league career, but also his 52.6% ground ball rate.

His power declined significantly in the second half, though, as his .576 slugging and .266 ISO in the first half dropped to .335 and .116 in the second half, respectively. Given his past performance in the minors, this was probably at least partially due to regression to the mean, but opponents may have also "figured out" Kiermaier. According to Brooks Baseball, he hit for the most power on pitches down and away last year, and while he saw a high frequency of these pitches in the first half, pitchers started throwing inside against him more after July 31.

While we can debate just how much his offense might regress, Kiermaier’s speed and defense aren’t going anywhere, so he will remain a valuable contributor for Tampa Bay going forward. Here is what the projections foresee.