What I look for depends on the defensive formation of my DC. Some generic traits:
- Defensive linemen and linebackers should be good at working off blocks. If my DE's Block Shedding rating is high and I'm playing as a LB, I am content with stringing out an outside run to give my computer DE a chance to make the play. With a lower Block Shedding, I feel the need to aggressively commit to making the play myself.
- Corners should be good coverage players in both man and zone. It is great if they can tackle too, but I'll accept "speed bumps" on the corner to slow the ball carrier enough for help to arrive.
- Safeties should be good tacklers and zone defenders. A lot of man coverage calls will have a single or two safeties in zone. Without a good zone defense rating, you may as well send the safeties on the blitz because they will almost always be late when helping a corner / LB.
- Linebackers (in addition to #1) should have good speed, which generally makes them Coverage LBs in this game. On 3rd and 5--11, zone coverage with these LBs will typically take the draw plays and short patterns (crossing / slants / mesh / etc) and help you get off the field. This forces your opponent to attack your secondary.
- I prefer tall DEs in addition to #1, I want them to be 6'4" or taller. A short, quick DE with good Block Shedding is acceptable, but not ideal.
- I prefer about 300 pound DTs in addition to #1. 330 pounders don't move well enough in general and are only good to stuff runs up the middle. I will only go after one (a JUCO) if my current year's team is vulnerable up the middle. JUCOs are expected to play a large role immediately in my dynasty universe.
I will play about 60% man coverage. I blitz on roughly 75% of the defensive play calls. The more zone you play, the more important the tackle rating is for all players. So regarding item #2 above, if I take over a team where the corners are good tacklers and OK in coverage, I will play more zone than man until I can build the team I prefer.