Why resting McCaffrey remains a challenge for 49ers coach Shanahan

There's no doubt Christian McCaffrey is a vital part of the 49ers' offense, but even the All-Pro running back needs a break at times. During the 49ers' 27-14 win over the Tampa Bay Buccaneers on Sunday at Levi's Stadium, Elijah Mitchell went into the game to start the third drive early in the second quarter. Mitchell carried the ball four times for 24 yards in that series and was on the field for five offensive plays. Mitchell only appeared on the field for three additional snaps, while McCaffrey carried the on-field load for 52 offensive plays, or 87 percent. On Monday, coach Kyle Shanahan shared how running backs coach Bobby Turner Jr. provides input on when to sub out McCaffrey and all of the factors that go into the decision. "That's when Christian had gone 18 plays in a row," Shanahan said. "Bobby will get on the headset and say, 'Hey Kyle, he's gone 18. I'm going to start this series out with Elijah. You good with that?' And I say, 'Yeah, go ahead.' " Mitchell was on the field for three straight carries early in the drive, and then on the fourth play - a third down - McCaffrey went back onto the field. One play later, Mitchell resumed his spot in the backfield for two plays...