Brent Rooker hit a milestone home run on Sunday, his 20th of the season accounting for Oakland’s lone run in a 12-1 loss to Baltimore. On Monday, the ex-Mississippi State star hit a much more significant home run, No. 21 producing a walk-off 6-4 victory for the A’s over Kansas City at Oakland Coliseum. Not only that, the homer came just in time for Rooker and some teammates to scurry over to the Oakland Arena and catch the show by Rooker’s favorite country music star, Zach Bryan. Rooker even made an appearance on stage with Bryan, who was performing before a crowd quite a bit larger than the 3,095 who watched the two worst teams in baseball fight to the finish on Monday. It has been a roller coaster of a season for Rooker, who joined the A’s as an off-season waiver claim from the Royals. He ht .358 with nine homers in April, which earned him an appearance on MLB Network’s MLB Central show and propelled him to his first All-Star Game nod. There have been a lot of struggles since then, but Rooker’s bat has perked up recently. He is hitting .346 over his last seven games. “Swing and approach-wise, I feel pretty solid,” he said. Rooker, batting .245 with 53 RBIs, and many of his teammates may be vying for 2024 jobs with the lowly A’s, who are 35-90. … Rooker stands second on the All-Mississippi Home Run Derby chart to Austin Riley, who has 29 this season. Hunter Renfroe is at 18, Nathaniel Lowe at 15, Adam Frazier at 13 and Matt Wallner at nine.