pressure every time...

In man the DBs usually-not always-play in inside leverage, just slightly inside the receiver--to take away quick slants. They don't want to trail the receiver in those routes.

By playing inside, you're allowing the receiver to go to the outside and trail him. That's the thing with man coverage you play trail technique, you follow him. And most receivers in the NFL are good enough to beat that coverage and the QBs are so accurate that they can make a throw that can be caught or draw interference---if they have time.

The only way to apply pressure enough is to blitz---It's rare to see just 4 guys rush the passer, so you need to send five or six, but that leaves no opportunity to double cover in man.

All I am saying is it's hard in these days to do it, receivers are bigger than CBs, usually, except for slot guys---and QBs are soo precise that even when coverage is good they can make a throw that has good shot at being completed. Man opens up back shoulder throws, which the CB cannot see because he's trailing.

And with all the running QBs when they see man coverage (can see the names on back of jerseys) they can just take off...

Now, there are teams that play man--here is a chart--all the blues are zone, the yellows and reds are man
but even the ones that play a lot of man are playing it maybe 1/4 to 1/3 of the times

look at Patriots last year, less man to man as the season went on. Miami only team that played a lot of man and they did it roughy 50-60%
Teams don't play a lot of man anymore---league wide it's about 25% according to PFF . . .

it's just too risky to play it a lot because it's so hard to get pressure, you have to blitz to make it work.