In Christian McCaffrey, the 49ers have arguably the best running back in the NFL. That didn't stop them from beefing up the position.On Saturday, they traded up in round four to take former Wisconsin and Louisville running back Isaas Guerendo with the 129th overall pick."Well we love his speed," coach Kyle Shanahan told reporters on Saturday. "We think he's got a lot of speed. All our backs can run, but it's nice to add one who possibly can run a little bit faster just for the change of pace and things like that. We like his running style. His running style I think is similar to Elijah [Mitchell] and the style that he runs with, he's built that way and like the 40 that he has."Guerendo ran a 4.33-second 40-yard dash at the Scouting Combine. But that doesn't mean the 49ers were targeting speed for speed's sake."We didn't make a blanket statement like that," Shanahan said, "but we wanted to add some speed to the running back room if we could. But you don't just add that just to add it. It's got to be the right type of runner with the speed. And there were a couple guys in the back end in the draft who had that. And this is the one we really liked in that way."Running backs coach...
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