I watched the WV clip. WV was 10-3 last season so they were a good division 1 club. Youngstown played them very tough, especially in the first half, and it was 21-31 in the middle of the 4th, and most of WV's offense came on long passes.
On Rivers specifically.
1. He's definitely a quick twitch athlete who can explode off the ball
2. That being said, most of the time he played a read technique on his OT.
3. I don't know who the WVU OT was, or if he was any good, but Rivers was never knocked off the LOS in any run play. He was consistantly lower than the OT and controlled him with his arms locked out, never letting the OT into his body, and this is a guy who clearly outweighed him by 50 or 60 lbs.
4. He had 4 QB hits in the first half, and 2 should have been sacks. And this was against a successful DI team's starting RT. In the 2nd half he wasn't as productive, but rarely had a chance to simply rush the passer.
5. On the negative side, twice in the 2nd half he was looking around when the ball was snapped.
Overall I was impressed. For a guy as light as he is, playing a straight 4-3 DE against a RT showed great functional strength and technique. Interesting that Polini never just let him loose to rush the passer in that game.
The Pats teach a similar read technique as their base defense, so Rivers should be familiar with it.
Short term I see River's best use would be as a situational pass rusher from the DE or OLB position. I'd love to just see him let loose, like Miller is in Denver, but that likely isn't going to happen. Long term he might get moved to OLB in the old Jamie Collins role, but I'm not sure. It will depend on his cover skills.
Loved the comparison of Mickinely and Rivers.