In 2008 Josh McDaniels was the New England Patriots Offensive Coordinator. He had previously been been with the Patriots since 2001, before being promoted to OC in 2006. Following a few successful seasons in New England McDaniels departed to coach the Denver Broncos. McDaniels was later fired by the Broncos and landed in St. Louis, where he coordinated the Rams' offense during the 2011 NFL season. Following the season McDaniels was let go by the Rams and immediately signed with his former team, the New England Patriots, and will be with the team during their home playoff game against – ironically – the Denver Broncos.
How can a coach join a team mid-playoff run? That's like an NFL free agent signing with a team immediately following the regular season only to join his new team during their playoff run. Unfair advantage, right? Well, according to ESPN's Adam Schefter the NFL will review the rule which allowed McDaniels to sign and join the Patriots mid-playoffs this off-season.
NFL will review rule this off-season that allowed Josh McDaniels to change teams in the same season and to coach in the post-season.