Mason McLendon Barnett was originally signed by Royals scout Will Howard…graduated from Cartersville HS (Ga.) in 2019, where he was a two-time Class 5-4A All-Region honoree and Cartersville High School Pitcher of the Year…attended Auburn University from 2020-22, where he struck out 142 batters in 111.1 innings (11.5 strikeouts per nine innings) across 41 appearances (20 starts) over three seasons…his pitching coach with the Tigers was A’s Hall of Famer and Auburn Alum Tim Hudson…made five starts with the Brewster Whitecaps in the Cape Cod League in 2021.
2025
Made both his Triple-A and Major League debuts in 2025…spent most of the season at Las Vegas, where he was 6-2 despite a 6.13 ERA and .801 opponents' OPS in 25 games, including 23 starts...was selected on Aug. 26 and went 1-1 with a 6.85 ERA and .816 OPS in five starts with the A's...Struck out 18 batters in 22.1 innings with the A's and walked 11 for a strikeout-to-walk ratio of 1.64...Allowed a .286 opponents' batting average, which broke down to .243 (9-for-37) with a .604 OPS against left-handed hitters compared to .315 (17-for-54) with a .961 OPS against right-handers…surrendered all three of his home runs to righties...Held the opposition to a .085 batting average with two strikes...The A's were 3-2 (.600) in his starting assignments…tossed five innings or fewer in four of his five starts…allowed at least three runs in all five starts...With Las Vegas, he struck out 124 batters in 119.0 innings and his average of 9.38 strikeouts per nine innings was the lowest of his Minor League career...Walked a career-high 65 batters for a career-high 4.92 walks per nine innings...Also had career highs in hits (125), runs (81), earned runs (81), home runs (17), ERA, opponents' OPS, batting (.265), on-base percentage (.360) and slugging percentage (.441)…Ranked third in the Pacific Coast League in strikeouts, seventh in innings pitched and tied for seventh in games started…issued the third most walks (65), was tied for third in balks (three) and ranked fifth in most pitches (2176)…averaged the most pitches per game among pitchers with 90 or more innings pitched (87.0)…Ranked fifth in the A's farm system in strikeouts, sixth in innings pitched, seventh in games started and tied for eighth in wins...Allowed a .265 opponents' batting average, which broke down to .262 (59-for-225) with a .780 OPS against left-handed hitters and .267 (66-for-247) with an .818 OPS against right-handers...issued 42 of his 65 walks and recorded 80 of his 124 strikeouts against right-handers...Opponents hit .263 with runners in scoring position...As a starter, had a .308 opponents' batting average the first time through the batting order, .201 the second time and .313 the third time...Was 3-0 with a 4.87 ERA in 12 games on the road, 3-2 with a 7.45 ERA in 13 starts at home…surrendered 11 of his 17 home runs at home. Compiled a 7.88 ERA and .876 opponents' OPS over innings 1-2, a 3.57 ERA and .661 OPS in innings 3-4, and a 7.39 ERA and .895 OPS from the fifth inning on...The Aviators were 15-8 (.652) in his starting assignments...tossed five innings or fewer in 18 of his 23 starts...walked at least one batter and yielded at least one run in all 25 of his appearances...Was rated as the A's No.9 prospect by MLB.com.
2024
Was acquired by the A’s at the trading deadline with two other players from Kansas City for Lucas Erceg...spent the entire season at the Double-A Level and combined for a 9-8 record, a 4.20 ERA and .701 opponents OPS in 26 games, including 25 starts, with Northwest Arkansas and Midland...Struck out 161 batters in 133.0 innings (10.89 strikeouts per nine innings) and ranked eighth in all of Minor League baseball in strikeouts...Placed second in the Texas League in strikeouts, tied for second in games started, third in innings pitched, fourth in ERA, tied for fourth in wins and fifth in opponents batting average (.240)...Had career highs in every counting category except walks and wild pitches...his ERA and his slashline numbers of .240/.316/.385/.701 were the highest of his three professional seasons...His opponents batting average broke down to .247 (74-for-299) with 10 of his 13 home runs and a .745 OPS against right-handed pitchers compared to .229 (47-for-205) with a .635...OPS against left-handers...Yielded a .220 average with runners in scoring position...opponents were 1-for-8 (.125) with a double and three strikeouts with the bases loaded...As a starter, had a .200 opponents batting average the first time through the order, .250 the second time and .312 with six of his 13 home runs the third time...Combined for a 3-6 record and a 5.62 ERA in 12 starts in his home ballparks...was 6-2 with a 3.11 ERA in 14 games, including 13 starts, on the road...Had a 1.44 ERA in the first inning and a 3.21 ERA over innings 1-4...logged a 6.94 ERA from the fifth inning on...surrendered seven of his 13 home runs in the fifth inning (8.44 ERA)...Was rated as the Royals fourth-best prospect by MLB.com at the time of the trade and was ranked as the A’s sixth-best prospect following the season.
2023
Barnett was the recipient of the 2023 Paul Splittorff Award, given to the top pitcher in the organization, as well as being named an MLB Pipeline Pitcher Prospect of the Year and MiLB.com Organization All-Star... He split the season between High-A Quad Cities and Double-A Northwest Arkansas, where he amassed a 3.30 ERA (42 ER in 114.2 IP) across 23 starts with a Royals Minor League-leading 137 strikeouts (10.8 K/9, 28.8 K%) and a 1.19 WHIP...across his 23 starts, he never allowed more than four earned runs, and following the MLB All-Star break, he went 4-2 with a 2.66 ERA (15 ER in 50.2 IP) over 10 starts... In Quad Cities, he went 4-6 with a 3.18 ERA (29 ER in 82.0 IP), 94 strikeouts (10.3 K/9) and an opponents’ batting average of .203, earning a promotion to Double-A Northwest Arkansas on Aug. 2... He made his Double-A debut on Aug. 8 vs. Wichita and struck out 7 batters over 5.0 innings...each of his next two starts came at Corpus Christi on Aug. 15 and 20, and he combined to cover 9.0 one-run innings with 12 strikeouts and just 6 hits across the two outings.
