Why are there never big mid-season signings in football as there are in baseball?

Hm...I guess I'd have a tendency to ask the question in reverse. Why does baseball have mid-season signings? ;)

In truth, they're very different kinds of sports. While both involve teams, baseball is primarily dependent on the individual's skills, while football is primarily dependent on trust between teammates. The quarterback and the receivers need to get to know each others' abilities and timing within a pass play. The defensive line needs to learn to work together, or else they're just a collection of men standing on the field. Mid-season trades would be devastating to the synergy that they have been working on.

I think your referring to trades. It can take a couple weeks to a few weeks to fully grasp the offense or defense. By that time, that player that the team traded draft picks for will have barely played and teams would know whether they have a chance at the playoffs or not.

Plus, salary cap concerns as well as how valuable those draft picks are come into play.

I guess guys like Herschel Walker and Eric Dickerson weren't big names.