I think the 11 minutes is a little low, DirectTV has a feature which cuts the game down to just the plays, (and some select replays) and they fit it in to a thirty minute time slot. I would put the average action to about somewhere between the 18-22 minute range.
Lets also remember that hockey shifts usually don't last longer than one minute. If anyone is on the ice for more than that, they are usually gassed. And even with that, it is not like they are skating up and down the ice five times in that minute. Football is full speed, full contact for a good seven to ten seconds (12 if your name is Mankins), then the rest and then back at it.
Hockey is a great game, but football is definatley more violent, in a typical game their are about thirty violent checks, in a typical football game there are seven violent collisions on each and every play.
Google..."nfl actual minutes"...and you will be able to read dozens of articles stating game time is between 11-12 minutes
As to your paragragh describing hockey shifts....clearly you don't know what you are talking about.
Back to NFL:
Average length of each play: 5.5 seconds
Remaining game clock allowed after each average length play: 39.5 seconds
Expanding NFL action/rest in NHL terms (5.5 secs NFL : 1min NHL) gets you 39.5 secs/395 secs. In other words, if NHL players rested the same proportion between shifts as NFL players rest between plays., NHL players would rest 6.5 minutes per shift. But since the typical NHL team uses 3.5 lines (4th line is used sporadically), NHL players get half the rest
Incidental Hits topic: I seem to recall that the amount of "incidental" hits vs Vancouver was about 2-3 per possession and 2-3 per forechecking. In other words, the battles were won and lost in the corners with bodies flying into each other continuously....and usually longer than 5.5 seconds.
Violent hits topic: certainly different angles of hitting ...with NHL players only able to throw punches at heads instead of arm tackles around pads. Curious, do you think violent hitting is occurring on the line when Brady goes back to pass 35 times per game. O linemen standing/fending off defenders trying to go around them. Seems Chara is acting in a similar manner defending in front of his own net....yet he can play 30 times more minutes over a season, 3 times a week over 9 months. Again my point is: I don't buy the NFLPA arguement that more than 16 games in a regular season is too many. Seems to me that the underlying reason that restricts more games is that NFL rosters are too small to begin with....basically 1.25 reserve players for every starter. The NHL has a 4:1 ratio, NBA 3:1.
By the way, did any one watch the college rugby 7s championships last week.....teams played 3 games a day plus on consecutive days. Imagine...continuous action, tackling, no pads, games every two hours....all weekend.