Depends on the situation. In football, the coaches and team captains have a lot of responsibility. That said, guys like an offensive guard don't have much to do. Baseball, on the other hand, is a series of lightning quick decisions.
I'd also argue that the average baseball player is likely more intelligent than the average football player.
Opposing teams/players have to get inside each others heads. The manager has to take into account how strong the opponents lineup is, what side the batters bat from, etc, etc.
The catcher has to recognize each batter's tendencies, how strong his pitcher is, and the umpires' quirks as far as calling pitches, and keep a watchful eye on any base runners on top of that. A pitcher must figure out where and how he must place his next pitch in order to get the next out. A pitcher must also follow a very certain routine before delivering a pitch, otherwise he risks being charged with a balk. The batter has to recognize what kind of pitch is being thrown his way (speed/break), decide whether or not said pitch is worth hitting and then getting his bat in front of the ball. Infielders and Outfielders have to know whether said batter tends to pull or push his hits and how far they tend to hit.
It is a game of constant adjustments, and as Spike said, a series of lightning quick decisions. Once you start bringing in the bullpen, pinch hitters and runners, the strategy gets real fun.
Football is more straightforward. It was more or less memorizing routes, and recognizing each other's types of plays and strategies and adjusting on occasion. Teams have to take into account whether a team likes to run the ball, air it out, or mix it up, and which players the QB tends to prefer tossing to. Football also has a clock to kill, which kind of kills it for me but adds to the strategery I suppose.
Both games have a lot of strategy, I just think baseball has more.
