Martin was Oakland's leading rusher in 2018, finishing with 723 yards and four touchdowns on the ground. His return to the Raiders comes shortly after ESPN's Adam Schefter reported Isaiah Crowell suffered a season-ending torn Achilles.
Even after they signed Crowell, the Raiders had a pressing need at running back entering the 2019 draft. Martin and Marshawn Lynch were free agents, with the latter potentially retiring from the NFL altogether.
Oakland selected Alabama running back Josh Jacobs in the first round to fill out its backfield and provide competition with Crowell for the starting job. When Crowell suffered the injury, the team's lack of depth at the position was once again glaring.
Although Martin's days as a team's primary ball-carrier are probably over, he can be a solid secondary option behind Jacobs in 2019.
Martin, who turned 30 in January, averaged 4.2 yards per carry last year and finished 39th in DYAR (defense-adjusted yards above replacement) among 47 running backs with at least 100 carries, per Football Outsiders.
At this point in the offseason, the free-agent market is pretty thin, and the Raiders didn't want to invest too heavily in a replacement for Crowell with Jacobs poised to play a big role in the offense. Signing Martin, who has experience working with offensive coordinator Greg Olson, was the most logical response to Crowell's injury.