As a freshman for the California Golden Bears in 2014, Jefferies started 15 games, finishing the year 2–8 with a 3.45 ERA and 58 strikeouts in a team-high innings. Jefferies' sophomore season saw both his record and earned run average improve, as he appeared in 14 games, starting 13, and went 6–5 with a 2.92 ERA, enough to warrant a First Team All-Pac-12 selection. The summer after his sophomore season, Jefferies was a member of the USA Baseball Collegiate National Team, and played collegiate summer baseball with the Wareham Gatemen of the Cape Cod Baseball League. Jefferies was drafted by the Oakland Athletics with the 37th overall pick of the 2016 MLB Draft. He spent his first professional season with the AZL Athletics where he posted a 2.38 ERA with 17 strikeouts in 11.1 innings pitched. He pitched in only two games for the Stockton Ports in 2017 before undergoing Tommy John surgery, thus ending his season. He appeared in one game in the AZL in 2018 as he continued to rehab his way back to full health. Jefferies split the 2019 season between Stockton and the Midland RockHounds, going a combined 2–2 with a 3.41 ERA over 79 innings. Jefferies was added to the Athletics 40–man roster following the 2019 season. Jefferies has a four pitch repertoire. His fastball has a bit of sink and sits in the low-to-mid 90s, but can top out around 96 mph. His primary off-speed pitch is his changeup which he throws in the mid-80s with good sink and fade. He also has a decent slider and a good three-quarters curveball. Jefferies is the nephew of former MLB pitcher Blas Minor, and his older brother Jake pitched in the minor leagues for both the Miami Marlins and Tampa Bay Rays organizations. Vimael Machin (born September 25, 1993) is a Puerto Rican professional baseball infielder in the Oakland Athletics organization. Machin attended Puerto Rico Baseball Academy and High School in Gurabo, Puerto Rico. He was drafted by the San Diego Padres in the 29th round of the 2011 MLB draft, but did not sign. He attended Virginia Commonwealth University and played four year of college baseball for the VCU Rams. In 2014, he played collegiate summer baseball with the Bourne Braves of the Cape Cod Baseball League. He was drafted by the Chicago Cubs in the 10th round of the 2015 MLB draft and signed with them. Machin split the 2015 season between the Eugene Emeralds and South Bend Cubs, hitting a combined .181/.270/.222/.492 with 10 RBI.