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After an initial rocky start with the X’s in 2019, Sierra became one of Sioux City’s most reliable arms. He appeared in a total of 25 games with thirteen of them being starts, collecting an 8-1 record and a 3.21 ERA over 95.1 innings of work. He struck out a total of 98 batters in that time for a K/9 of 9.1. 

The aforementioned rocky start came in his first twelve appearances out of the bullpen that can be attributed to some bad luck. Sierra carried a 5.06 ERA into June 19th, despite striking out 27 batters over 21.1 innings and walking only seven and holding a WHIP of 1.17. 

After a five inning shut out performance in relief, Sierra would be given the opportunity to start. He made the most of the opportunity and helped sure up the X’s rotation. In thirteen starts he threw 74 innings, striking out 69 batters and holding together a 2.92 ERA as a starter.

He began his career pitching for the Sancti Spiritus of the Cuban National Series where he posted a 3.68 ERA in 14.2 innings as a 19 year old. Unlike many of his other native Cuban players did not need to defect his home country to be able to establish residency and play baseball outside of the country. He was granted Spanish citizenship due to his grandfather’s roots allowing him to leave Cuba legally. He then pitched in the Canary Island for the Tenerife Marlins in the Division de Honor de Beisbol the best league Spain has to offer.

He signed as an international free agent with the Houston Astros on December 24^th, 2015. His first season in affiliated ball began late in June of that season but Sierra pitched well for the Astros Low A club mostly appearing out of the bullpen. It earned him a late season promotion to the Quad City River Bandits of Davenport, IA. In only 10 innings, he was able to hold an ERA of 1.80 while striking out 16.

Dominating A-Ball once again Sierra earned himself a quick promotion to High A during the 2017 season spending most of the year pitching for the Buies Creek Astros of the Carolina League. He would make 25 appearances for the Astros pitching 48 innings, going 3-1 with a 3.00 ERA and 49 strikeouts. Add in his 11 punch outs with Quad Cities earlier in the year in 9.1 innings, and Sierra’s 60 strikeouts that season are still his career high.

The 2018 season took place in Buies Creek and he once again showed Houston that he had mastered that level with a 3.32 ERA in 10 appearances, with 21 strikeouts in 21.2 innings. He was then promoted to AA Chorpus Christi there he pitched in 16 games and 21 innings with a 6.00 ERA. The Houston Astros released Sierra in March of 2018.

Sierra did not play during 2020.