By Kyle Wood It might be a battle of the backups when the Broncos welcome the Cardinals in Week 15. Denver is a small home favorite. Two of the worst teams in the league play one another Sunday and they might both be trotting out backup quarterbacks. Cardinals quarterback Kyler Murray tore his ACL in the first quarter of Monday night’s loss to the Patriots, which ended his season. Backup Colt McCoy took Murray’s place under center. Broncos quarterback Russell Wilson entered concussion protocol during a home loss to the Chiefs in the midst of one of his best games of the year and Brett Rypien r…