Can't trade rookies?
 

When I try to trade a rookie, I get the message, "Your opponent is unwilling to trade for someone you just signed." I seem to recall this being around in previous versions too.

Yes, it's always been this way. The game won't let you pull the sign and trade. I'm not sure if it mimics real life or not.

There's no rule prohibiting this in real life, but it is very rare to see in the NFL. What you don't want in a text sim is the ability to offer a bunch of bonus-free deals to top free agent players, only to turn around and trade them away for draft picks. This simple rule clearly keeps that from happening (though occasionally an AI team will approach you about a just-signed free agent, and AI-offered trades just get acepted, without checking for the various consequences like salary cap, offsetting value, or this). A little clumsy, yes, but it prevents a major loophole.

exactly. A necessary evil in this case.

circa 1989

Lions: How come nobody wants to trade us for Barry Sanders?

Other Teams: Cause you just signed him as a rookie. We can't possibly take a gamble that he will work in our offense.

Lions: sigh