Head coach Chip Kelly said it was his understanding that right tackle Anthony Davis retired Monday because of “injuries,” but he did not speak to him about his decision to leave the NFL for the second time in 15 months. Davis, who had missed the past two games after sustaining a concussion in practice, said on Twitter on Monday that wanted his “mind intact.” Davis left the NFL after an injury plagued 2014 season in which he missed four games with the first concussion of his football career. [...] Kelly said left guard Zane Beadles would continue to assume Davis’ former spot as the emergency tackle and guard/center Marcus Martin and rookie guard Joshua Garnett would remain the backup linemen on game days. Beadles played tackle at Utah and started six games at right tackle for the Broncos as a rookie in 2010.