In fact, it already has happened this season.
After Raheem Mostert went down in the season opener with what would turn out to be a season-ending knee injury, Shanahan turned to rookie Elijah Mitchell, a sixth-round draft pick out of Louisiana Lafayette. Mitchell promptly trampled the host Detroit Lions for 104 yards and a touchdown in a 41-33 win.
During last week’s 17-11 win at the Philadelphia Eagles, Mitchell suffered a shoulder injury and briefly had to leave the game. He did not practice this week until Friday and is listed as doubtful to play against the Packers.
That was hardly the only calamity to strike the position in Philadelphia, though. Trey Sermon, a third-round pick who was making his NFL debut, suffered a head injury on a scary-looking hit and tumble on his first carry. He was taken out of the game and placed in the league’s concussion protocol. Sermon returned to limited practice this week and was medically cleared to play Sunday, but another 49ers back, second-year player JaMycal Hasty, is probably out for several weeks after suffering a high-ankle sprain against the Eagles.
Then there’s fourth-year back Jeff Wilson Jr., who led the team in rushing last year but is starting this season on the physically unable to perform list after suffering a torn meniscus in the offseason. In response to the recent injuries, San Francisco signed running back Jacques Patrick, who has yet to play a down in the NFL, off the Cincinnati Bengals’ practice squad and added veterans Kerryon Johnson and Chris Thompson to its practice squad. Earlier, when Mostert got hurt, the 49ers signed little-used veteran Trenton Cannon after he was released by the Baltimore Ravens, who have undergone their own rash of injuries at the position.
“It alters a lot because you have to make sure you give different options in every situation,” Shanahan said Wednesday of the uncertain situation with his running backs. “Especially when there’s a lot of unknown. There’s a chance we might only be down one compared to last week. There’s a chance there might be a whole new group, which would be down to our sixth on the year. So you have to plan for everything, and that’s what you do.”
The good news is that Shanahan, after apprenticing under his father and others, has shown he can conjure a running game with whoever happens to be available. Since 2012, with Shanahan serving as either an offensive coordinator (Washington, Cleveland, Atlanta) or a head coach (San Francisco), his teams have finished in the top 10 in rushing yards five times and in the top 15 seven times and were never worse than 21st.
During that 10-year span, his leading rushers have been: Alfred Morris, a sixth-round pick out of Florida Atlantic; Terrance West, a third-round pick out of Towson; Devonta Freeman, a fourth-round pick out of Florida State; Matt Breida, an undrafted free agent out of Georgia Southern; Mostert, a UDFA from Purdue; and Wilson, a UDFA from North Texas.
Few were better at turning unheralded backs into effective NFL players, if only for a season or two, than Mike Shanahan. From 1989 to 2013, over stints as the offensive coordinator in Denver and San Francisco and the head coach in Oakland, Denver and Washington, his teams finished in the top 10 in rushing yards in 19 of 23 seasons. With the Broncos, he helped send to the Pro Football Hall of Fame running back Terrell Davis, a sixth-round pick out of Georgia. Other backs who made a splash on Shanahan’s teams included Olandis Gary, Mike Anderson, Reuben Droughns, Selvin Young and Roy Helu.
Apart from familial bonds, the thread that runs through the Shanahans’ annually strong running games is their use of outside zone schemes, in which offensive linemen move laterally at the snap and block whomever winds up in their paths rather than specific, predetermined defenders. Running backs then follow those blocks and use cues to determine where to hit a crease. These schemes force the defense to move laterally rather than upfield, which in turn buys time for the quarterback on passing plays.
Kyle Shanahan’s 49ers use play-action extensively, and those play calls can be all the more potent when combined with boot action, in which the quarterback rolls out in the opposite direction of the running back and takes advantage of over-pursuit by confused opponents. That feeds back to the running game because the defense needs to account for plays going in either direction horizontally and thus tends to be stretched thin, often providing clear holes for the one-cut-and-go style the Shanahans have generally emphasized to their backs.
The results have been remarkably consistent over a number of decades and a father-son passing of the coaching torch. In case after case — even, arguably, with Davis — it has been reasonable to conclude that the system made the back rather than the other way around.
So don’t be surprised if and when the 49ers turn a shorthanded situation at running back into a steady stream of long plays.