What it means that Patrick Willis is switching from 'Mike' role to NaVorro Bowman 'Jack' role

Yesterday during 49ers OTAs it was revealed that Patrick Willis has been approached by the team to play the position vacated by NaVorro Bowman as the latter heals from his injury. To some of us, this might seem odd, as we may view the ILB positions in a 3-4 defense as nearly the same, and perhaps it also seemed only logical that Willis (the best/tied for best ILB on the team) would simply take over for Bowman. But as Willis noted, there are nuances to the positions that he and Bowman play.

Willis typically plays "Mike" linebacker. This is the guy who plays the run and is generally moving forward after the snap. That's not to say Bowman doesn't also play the run, but his role of "Jack" entails a bit more responsibility and flexibility of assignment on any given play. Editor's Note: There have been several articles about this topic, and there is some confusion about whether Bowman played Jack or Mike. Our belief is that he played Jack, based on the details below, but it's possible teams can use LB names in different ways.

Depending on where you look, you'll see the Jack often described as an outside linebacker who rushes the passer, plays coverage, contains the run, etc. A "Jack" of all trades, but notice many cite this as an OLB. It's been compared to the Elephant position of a 4-3, too. A guy who's perhaps too small to play full-time DE but is large enough to go up against OLs from time to time as a pass rusher.

Clearly Bowman doesn't play OLB in the 49ers' 3-4 defense, but he was an OLB in Penn State's 4-3 and is adept at rushing the passer (as St. Louis found out in a game I attended last September). Bowman is a jack-of-all-trades, but he plays the Jack from the inside, not the outside.

Perhaps this is a little twist that Fangio put in when when the Niners moved Bowman into the starting lineup Fangio's first year with the team. Typically he's charged with going where the defense expects the ball to go. If a team likes to use it's TE in the passing game a lot, Bowman is usually the guy covering him. He'll also spy a key player at times, tasked with shadowing him and not letting him make a play.

Willis put it as:

You just tend to be a little more in the mix in terms of the (opponents') offensive strength.

The good news? Willis manned this position during his first several years with the 49ers, basically up until the point when Bowman arrived. We all remember Pat covering TEs and being all over the field when Takeo Spikes was with the team, etc. I don't think it will be any problem for him to slide back into the role.

One might think that the biggest drop-off will probably be in coverage, as Bowman has proven to be quite good there. However when looking at PFF's grades on the two, both finished 2013 with the same grade in coverage: +7.0. In fact, Willis actually graded better than Bowman in 2012, as well.

I think there's more to it than the numbers/grades here, though. Bowman, to me, appears to be the better cover LB, though Willis is certainly no slouch. At any rate, I don't expect much, if any, drop-off at the position, whichever position it is.