When watching film on Mike Mitchell, two things immediately jump out at you.
First, he is fast. Being fast in the NFL is all about how quickly you can accelerate. How long does it take you to get to top end speed? For, Mitchell, the answer is not long. He has an explosion and a burst to the football. That burst can sometimes be his greatest enemy, the negative consequence being the occasional missed tackle. The Steelers have another safety that sometimes misses tackles because he forgets to take his foot off of the gas, and they seem to be pretty happy with him.
While it would be foolish to try to compare the two, but the point is Mitchell might miss a tackle or two. But, he is also going to make some plays for a Steelers defense that badly needs them.
The second thing that catches your eye about Mitchell is that he is smart. First, he takes great angles. In watching Carolina from last year, it was hard to find examples of Mitchell being challenged deep. He plays the deep safety position very well. Mitchell also takes good angles in the run game. Also, Carolina put Mitchell all over the field. Sometimes, you would see Mitchell lined up as their Will linebacker in their 4-3 defense. In short yardage, Mitchell would line up as the end man on the line of scrimmage, and blitz from that edge. Mitchell would sometimes play as a deep half safety, and he would sometimes be the single safety playing 25 yards deep. Mitchell blitzed often, and he disguised coverages well. Once again, he was all over the field.
Here is Mitchell playing a traditional strong safety:
Carolina shows a two high safety look, but at the snap, Mitchell begins to spin down while the other safety drops. Mitchell is the force player; meaning, he cannot allow the ball carrier outside of him. Mitchell shows the necessary speed to hold this play to a minimal gain. This is exactly how you want a safety to play the run. Read the end man on the line of scrimmage for a run/pass key, attack downhill with proper leverage, and then finish the play.
This is an example of a play that has been missing from the Steelers defense:
New Orleans is going to send 4 receivers deep against Carolina's 2 high safeties. The safety at the top of the screen seems to be taking away the tight end's vertical route. On the bottom of the screen, however, there are three vertical threats against one deep safety. The corner is looking at the QB to see if there is a threat to the flat. Since there isn't he trails the receiver.
Lance Moore bursts off of the line of scrimmage, past the linebacker who is dropping into the hook area. Once Moore hits the 5 yard line, he is open because the linebacker does not continue to get depth with his drop. At this point, Mitchell is in perfect position. He is on top of Moore because Moore is the exact middle of the three receivers. Mithcell has divided all three receivers. Drew Brees tries to throw the ball on a line, away from Mitchell. Moore makes a good adjustment to the ball, but Mitchell times his hit perfectly. Thus, it is an incomplete pass.
If Brees had decided to throw the ball to the receiver at the bottom of the screen, he would have had to put more air under the ball, and it would have been a longer throw. Thus, Mitchell would have had more time to react to that throw. Contrast Mitchell with the other safety from Carolina. He does not get depth. Instead, he opens his hips towards the receiver running the bender route (running vertically then bending towards the other side of the field). Because he does not get depth, the tight end is open. If Brees puts some air under the ball and leads the tight end towards the back corner of the end zone, it is a touchdown.
As I mentioned, Mitchell does miss some tackles:
Because it is a draw play, Mitchell gets a high hat read from the offensive tackle. Therefore, once he realizes it is a run, he has a lot of ground to cover. Moreover, Frank Gore is outside of the tackle box so the defender is at a big disadvantage. Mitchell does not do himself any favors because he gives Gore too much room. As a defender, you want to close down as much distance as possible between yourself and the ball carrier. 5 yards is too much; ideally, you would want two yards. Then, you want to tamp your feet so that you can change direction with the ball carrier. Mitchell, instead, stops his feet and lunges. He does not do a good job of gathering himself and coming to balance. Notice, even though Mitchell misses, he misses outside in. Thus, the rest of the defense is able to get to Gore and prevent an even longer gain. Honestly, I am not greatly concerned about Mitchell missing a ton of tackles. I saw him make a beautiful open field tackle of Darren Sproles.
In summary, Mitchell gives the Steeler defense a lot to work with in 2014. His combination of speed and smarts will be an asset.