Zachary James Thornton was born May 19, 1988, in Oak Park, California. In the SoCal sun, Zack honed his baseball skills and demonstrated a great deal of proficiency playing America's pastime. By the time high school arrived, it seemed that youngster might just have a future ahead of him. Attending Oak Park High School, the six-foot student excelled in baseball, earning all-state awards for his performance on the diamond. Upon graduating from high school, Thornton attended Ventura College, alma mater of, among others, Mets alumni Darren Reed and Brandon Knight. In his sophomore year, 2008, Zack appeared in 13 games, compiling a 11-1 record with a 1.12 ERA in 89 innings. The San Francisco Giants selected Thornton with their 43rd round pick (1,287th overall) in the 2008 MLB Amateur Draft, but the youngster elected not to sign with the team, instead transferring to the University of Oregon to continue his academic studies and hopefully improve his standing in future drafts.
The gambit failed in a sense. Zack struggled with shoulder problems in his junior year and made a generally poor showing for himself in his first year playing for the University of Oregon Ducks. Appearing in 15 games, he finished the year with a 0-1 record, posting a 6.17 ERA, striking out 16 batters and walking 15 in 23.1 innings. He forewent the draft and went into his senior year, 2010, knowing that it was his last time to impress MLB clubs. The young right-handed did just that, however. Fully healed from the problems that plagued him the year before, Thornton had an excellent season for the Ducks, and is considered a key reason the school made its NCAA regional berth that year. Making 12 starts and appearing in 17 total games, Zack had a perfect 9-0 record, posting a 3.40 ERA, striking out 73 batters and walking 16 in 90 innings.
With their 23rd round pick (695th overall) in the 2010 MLB Amateur Draft, the Oakland Athletics selected Thornton. The 22-year-old quickly came to terms with the A's and was assigned to their Rookie-level MiLB affiliate, the AZL Athletics (Arizona League). He made three appearances for them out of the bullpen before being promoted to their Low-A affiliate, the Vancouver Canadians of the Northwest League. He made 15 appearances there, all out of the bullpen. He tossed 26.2 innings and posted a 2-2 record with a 4.39 ERA, striking out 29 batters (9.8 K/9) and walking 8 (2.7 BB/9).
Thornton began the 2011 season with the Burlington Bees of the Midwest League, Oakland's A-ball affiliate. In 83 innings, the 23-year-old posted a 2.39 ERA, striking out 82 (8.9 K/9) and walking 22 (2.4 BB/9), good for a spot on the Midwest League All-Star team. He had a brief cup-of-coffee with the Midland RockHounds, Oakland's Texas League AA-ball affiliate, but the season ended with Zack getting only one appearance. Instead of staying with the RockHounds for the 2012 season, he was instead assigned to the Stockton Ports, Oakland's California League Advanced-A affiliate. Though his 4.53 ERA is much higher than one would want, his peripheral numbers were better than ever. In 53.2 innings, he struck out 70 batters (11.7 K/9) and walked 19 (3.2 BB/9).
After the 2012 season ended, Oakland traded Thornton to the Pittsburgh Pirates, receiving back veteran MLB reliever Chris Resop. The Pirates initially assigned the 25-year-old to their Advanced-A affiliate, the Bradenton Marauders of the Florida State League, but quickly promoted him to their AA affiliate, the Altoona Curve of the Eastern League, and not long after that, to their AAA affiliate, the Indianapolis Indians of the International League. At every stop along that 2013 journey, Thornton excelled. With the Marauders, he posted a 1.93 ERA in 14 innings, striking out 14 (9.0 K/9) and walking 1 (0.6 BB/9). With the Curve, he posted a 2.00 ERA in 36 innings, striking out 45 (11.2 K/9) while walking 7 (1.8 BB/9). With the Indians, he posted a 3.91 ERA in 25.1 innings, striking out 31 (11.9 K/9) while walking 4 (1.4 BB/9). All in all, for the season, he pitched 75.1 innings and posted a 2.63 ERA, striking out 90 batters (10.8 K/9) and walking 12 (1.4 BB/9).
Zack pitched in the Arizona Fall League, posting a 3.07 ERA in 14.2 innings with a 8.6 K/9 rate. He was eligible for the Rule 5 Draft this past winter and left unprotected, but no club with room on their roster sought to add his services to their MLB team. As a result, he began the 2014 season with the Pirates once more, assigned to Indianapolis. The 26-year-old was off to a solid start: In 7.1 innings, Thornton so far has a 1.23 ERA with 8 strikeouts (9.8 K/9) to 1 walk (1.2 BB/9).
Despite posting the numbers that he has in his minor league career, Zack has surprisingly run-of-the-mill stuff. His fastball sits around 90 MPH, but doesn't get much faster. He compliments the pitch with a change-up that features roughly a 10 MPH differential from his fastball and a high 70 MPH slider. Because of the angle that he throws his pitches and because of natural sink that he imparts in his pitches, Thornton combines a fairly high strikeout rate with a roughly 50% groundball rate for his career. One of the likeliest sources of his success is how he throws the ball- across his body, from a low ¾ arm slot. The deception that that creates certainly can be among the primary reasons for his high strikeout rate, but he doesn't seem to be all smoke-and-mirrors; his control, low line-drive rate over the course of his career (14.7%), and ability to keep the ball in the park certainly do not stem from it.
Because of the way he pitches, lefties have had an easier time picking up the ball from his hand, and as a result, Thornton has exhibited slight platoon splits over the course of his MiLB career. Left-handed hitters hit .243/.294/.341, while right-handed hitters hit .202/.251/.298. Most significantly, his line drive rate is higher against lefties (19.2%) than it is right-handed batters (11.2), resulting in a higher BABIP. The differences in his strikeout rate and walk rate are otherwise negligible.
Depending on whether or not the Mets feel that Thornton is ready for MLB caliber hitters or not, he will either debut with the organization on the big league club to help bolster the bullpen, or the Las Vegas 51s.