Players retiring prematurely happens more than one might think. Rookie QB Eric Couch was one player who retired after signing a rookie contract and before a regular season game. He's still guaranteed all the bonus money that was promised him. Teams can in some instances, go after some of the signing bonus (as previously mentioned) through arbitration via the "Barry Sanders Rule".

Bonus money is just that, a bonus. It's extra money you promised a player to sign a contract with your team. How the league figures it into restricting the owners, known as cap, is not the players concern.
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Example:

(GM) - "Hey kid, I think your pretty good.

(Kid) - Thanks

(GM) - What do ya think about playing for our team. I'll pay you $100 per regular season game. That's $1,600 per season and the league will even give you extra $$ per playoff game. Heck I'll do that for 3 seasons if you'd like. What do ya say kid?"

(Kid) - Well, I'll have to think about it.

(GM) - I'll tell you what kid. I'll give you $1,000 right now if you sign this contract on the table right here. It's yours to do whatever you want with it..

(Kid) - I can buy a car with it? Or give it to my mom?

(GM) - Sure kid. Whatever you want. It's yours. Just sign right here.
But you have to make the team to get game checks from us.
And we have to play in the playoffs for the league to give you those checks.
So kid, What do ya say?

(Kid) - What if I get hurt or can't play?

(GM) - We still pay you game checks as long as your on the team. And you can't be on the team until you sign right here. And I'm gonna give you an extra $1,000 just to sign right here.

(Kid) - Ok it's a deal.

(GM) - Great. Sign here and here's your $1,000. I hope you make the team. Good luck

Note: Obviously a dummied down example but you get the picture. The kid has to worry about making the team to get game checks and the GM has to worry about getting the kid signed and working within the cap restrictions set forth by the league and agreed upon by the owners.

No wonder some teams have so much cap space with these $1600/year deals!

Lol.

LOL yeah that RB with a 4.9 avg and a rating in the 80's is not worth resigning.

Resurrecting this thread for a question...

After the last game of the regular season, isn't it in the league rules that a current year contract can't be renegotiated?

In other words, if I want to use the Renegotiation Wizard to try and retain players at this point, shouldn't the available Salary Cap / Number of Years / etc... Be based off of 2030 as opposed to 2029?

Not until the season switches to the next year.

So that would be after the "2029 End Of Season" sim, AKA the first week of 2030 Free Agency when the guys I'm trying to renegotiate with are out in the open? Heh.

If they accept a contract at the end of season sim that first season will go against 2029, so once the end of season sim as rolled over they will already be in year 2 of their contract.

Yeah, that's why I said after the "End Of Season" sim... I'd rather not have to renegotiate 2029 when I don't need to, but to get to 2030 being the first year, I have to risk losing my guys in free agency. Should be fun. Heh.

But my main question was about the 'disconnect' between the NFL rules and what we have here. I can't even find where I'd seen that the NFL had a rule in place to prevent negotiating current-year contract language after the end of the regular season, so I won't push this. :)

True, but even with the updates the elite players in this game ask for a far lower percentage of the cap than an elite player would ask for in the NFL.