Running back Zac Stacy, who got the nod over Richardson for the starting spot against the Jags, went down with a rib injury and did not return to the game, per ESPN's Nick Wagoner:
Stacy had a productive outing with 14 carries for 78 yards, but Richardson nearly got an identical amount of touches with 13 carries.
Richardson only posted 48 yards on the afternoon, but it's safe to say he would have made a much bigger impact on the fantasy football world had he been the guy from the get-go.
It's unclear at this point how serious Stacy's injury is, but should it set him back this week in practice, it's entirely possible that Richardson gets his starting job back—regardless of whether Stacy misses any games.
It is worth noting that Richardson has struggled to say the least in his starting role, with no touchdowns and a lowly 2.7 yards per carry through five contests. Also, Stacy had only one carry for four yards on the season prior to Week 5, so his productive day might give Jeff Fisher and his coaching staff enough to put their faith in him as a spark to the run game.
But Richardson brings a ton of speed to the table, which always makes him dangerous for big plays to the outside, in contrast to Stacy's power running style.
The Rams' backfield is hard to gauge at the moment, but Richardson looks to be the most relevant one in fantasy. Albeit as a flex option or bench back in most traditional leagues.