SANTA CLARA, Calif. (AP) — The San Francisco 49ers began their on-field work in the offseason with a surprise participant and a predictable absence. Star pass rusher Nick Bosa took part in the voluntary portion of the offseason for a change after spending previous seasons working out on his own in Florida, while receiver Brandon Aiyuk remains away from the team as part of a contract dispute. “It’s something that’s part of the business,” coach Kyle Shanahan said Tuesday about Aiyuk’s absence. “Anytime it’s part of the business part, you try to respect it. Stay out of as much as possible and look forward to the days when you can just focus on football.” Bosa skipped last year’s voluntary workouts as he sought a new contract, and spent most of the 2021 and 2022 offseasons back home in Florida, after missing the 2021 offseason rehabilitating a knee injury and the 2020 offseason because of the pandemic.