After delivering their best offensive season in 14 years, the Raiders have decided to let go of the coach who was responsible for putting that offense together.

According to NFL.com, the team has decided not to retain offensive coordinator Bill Musgrave. Musgrave's contract was set to expire at the end of the 2016 season and the Raiders have decided not to renew it.

Bay Area radio host John Middlekauf has reported that Musgrave will likely be replaced by Raiders quarterbacks coach Todd Downing.

The decision to give up on Musgrave was a surprising one, considering what he's done during his two years in Oakland. Before the 2015 season, Musgrave was hired to take over a Raiders offense that ranked last in the NFL in 2014.

During his first season, the Raiders moved from 32nd to 24th in total yards. In 2016, the offense exploded, and jumped up from 24th to sixth in total yards. The ranking was the Raiders' highest since 2002, when they had the top offense in the NFL.

The Raiders also saw a dramatic improvement in their points per game. Without Musgrave in 2014, they ranked 31st. With Musgrave, they ranked 17th in 2015 and seventh in 2016.

Of course, any Raiders fan can look at those numbers and credit the offensive revival to Derek Carr, who has blossomed into a star quarterback over the past two seasons. Although it's easy to give Carr credit for the success of the Raiders offense, it's worth noting that he struggled big time during his rookie year in 2014 without Musgrave.

It's very possible that Raiders coach Jack Del Rio decided to go in a different direction because he was growing frustrated with Musgrave. Over the past few weeks, Del Rio seemed to take small jabs at the Raiders' play-calling.

For example, after the team's regular season finale, Del Rio complained that Latavius Murray didn't get enough carries in Oakland's 24-6 loss to Denver.

Del Rio with a swipe at OC Bill Musgrave: "Latavius has only five carries. How does that happen?" — Vic Tafur (@VicTafur) January 2, 2017

No matter how successful you are, if you're not on good terms with the head coach, you're probably not going to last long anywhere.

As for Musgrave's replacement, Downing has had some sort of NFL job since 2003 when he was hired by the Vikings. The 36-year-old has been with the Raiders since 2015. Before that, he spent time with the Bills, Lions and Rams.