He previously served as an assistant coach for the Houston Texans, San Francisco 49ers, Miami Dolphins, Washington Redskins and the Chicago Bears.

[1] In 2006, Day was hired as an offensive quality control coach at the University of Michigan, where he worked with future NFL quarterback Chad Henne.

[2] He was recommended for the job by Chicago's offensive coordinator Mike Martz, with whom Day had worked with for two seasons in San Francisco.

On January 23, 2014, Day was hired by the Washington Redskins as their assistant offensive line coach.

[8] On the heels of a Chargers loss in their AFC Wild Card game against the Jacksonville Jaguars where they blew a 27–point lead, he and offensive coordinator Joe Lombardi were both fired on January 17, 2023.