RB: Broad Jump & Vertical jump
There are a variety of styles when it comes to running backs, so depending on what style of back you have, there are some drills that are more important than others. However, one common trait that most of the top backs in the league are great to elite explosiveness.
If you look at the top running backs like Derrick Henry, Christian McCaffrey, Alvin Kamara, Saquon Barkley, and Nick Chubb, they all possess this. Even Dalvin Cook, who bombed the combine for a reason I still don’t understand clearly, has elite burst and explosiveness when you watch him play.
Each of these players (besides Cook) posted a broad jump in the 70% percentile or above, along with a vertical in the 80% percentile or above. Hence, there is a decent correlation among the top performers at the position.
Only one of these guys ran a sub 4.4 in the forty-yard dash, and that was Barkley. So even though the elite speed is an excellent trait, the explosiveness seems more vital.