The Rangers originally signed Leclerc out of the Dominican Republic in November of 2010. He was quite successful at the lower levels of the system and reached Double-A in 2015 at the age of 21. Used as a reliever in previous seasons, he moved to the rotation in the Texas League but struggled (5.77 ERA in 22 starts).
In 2016 he returned to the bullpen and was much more effective, posting a 2.72 ERA in 43 innings in Triple-A with a 50/28 K/BB. Promoted to the majors, he pitched down the stretch with the Rangers with a 1.80 ERA, albeit with poor control.
Leclerc ranked 13th on the 2017 Texas Rangers Top 20 prospects list with the following comment:
13) Jose Leclerc, RHP, Grade C+: Age 23, signed out of Dominican Republic in 2010; posted 3.00 ERA in 66 innings between Double-A and Triple-A, 78/38 K/BB, just 40 hits; posted 1.80 ERA in 15 major league innings but with ugly 15/13 K/BB; fastball between 88 and 98 averaging 94; mixes in slider/hard curve and occasional change-ups; can be overpowering but command, control remain troublesome; ETA 2017.
The 6-0, 190 pound right-hander posted a 3.97 ERA in 11.1 innings this spring with a 13/6 K/BB. So far during the regular season he has performed well, throwing 3.2 shutout innings in three games, allowing one unearned run on just one hit, walking nobody, and fanning five.
Leclerc has topped out his fastball at 97 MPH this year. So far, he is using his mid-to-upper-80s secondary pitch more often this season than he did last year, granted the sample size is minuscule. The secondary pitch is reportedly a splitter/change-up, but it has so much movement that it is often mistaken for a slider. He will also break out a slow curve on occasion.
This video clip from Prospect Pipeline is two years old but shows how nasty Leclerc can be when his command is on:
From his major league debut:
If he maintains his control at the current level, Leclerc will be a dominant reliever and could close games eventually.