Why are the Cowboys starting Barham at inside linebacker? There could be a number of reasons, but I'd say one of them is his ability to cover a lot of ground quickly from sideline to sideline, like on this play.
Any fellow Texas high school football fans out there? For context on this play, the running back for Oklahoma is Tory Blaylock, son of former NFL running back Derrick Blaylock, and true freshman for the Sooners. The reason I bring him up is to point out his speed. Blaylock ran a 10.62 100-meter dash as a junior, and won a state championship in the 4x100 relay that same year which also set a national record by more than two tenths of a second at 38.92 seconds. Long story short, he is very fast.
Based on Barham's movements on this play when Blaylock goes in motion, it looks like he's manned up against him. The motion is to get Blaylock moving early and let him get to that top-speed quicker, and he looks to have a bit of a head start on Barham moving to the left. Barham's angle, however, eats up a lot of that space quickly, and he's able to recover and get out into the flat to take away what could've been an easy touchdown had he not gotten there in time. Instead, the Sooners were faced with fourth and goal.