Holmes went 10-9 with a 4.22 ERA in 26 starts for Double-A Altoona this year, his first full season since undergoing Tommy John surgery in March 2014. Holmes pitched 136 1/3 innings, striking out 101 while walking 64.
He pitched particularly well in the second half of the season, posting a 3.03 ERA while limiting opponents to a .639 OPS over his last 14 starts. It was an encouraging sign for Holmes, selected in the ninth round of the 2011 Draft.
The 6-foot-5 Holmes does a number of things the Pirates value in a starting pitcher. Specifically, he pounds the bottom of the strike zone with fastballs to generate ground balls, recording 2.94 outs on the ground for every out in the air this year -- the highest ratio among all full-season Minor League pitchers and the second-highest in all of Minor League Baseball.
With the addition of Holmes, the Pirates' 40-man roster is full. They are carrying 19 pitchers, four catchers, 12 infielders and five outfielders. To sign a Major League free agent, they will have to remove someone from their roster.
Four players who would have been eligible for the Rule 5 Draft -- Adam Frazier, Chad Kuhl, Steven Brault and Trevor Williams -- were already on the Bucs' 40-man roster after making their Major League debuts this year; the Pirates also added potential Minor League free agents Jose Osuna and Dovydas Neverauskas earlier this month.
The most intriguing prospects left unprotected by the Pirates are outfielder Barrett Barnes and third baseman Eric Wood.
Barnes, their No. 26 prospect, hit .306/.377/.477 in 124 games for Altoona and can play all three outfield positions. But Barnes, drafted 45th overall in 2012, has spent five seasons in the Pirates' system without advancing past Double-A.
Wood, 23, has put together a strong showing in the Arizona Fall League after batting .249/.339/.443 in 118 games for Altoona.
Pittsburgh's only other top prospect left unprotected is right-hander Dario Agrazal, ranked 24th in the Bucs system. Agrazal, 21, went 8-12 with a 4.20 ERA over 27 starts for Class A West Virginia this year.
The Bucs did not select anyone in the Major League phase of last year's Rule 5 Draft, and they lost only one player: reliever Deolis Guerra, who had been signed to a Minor League contract shortly before the draft took place.