Well, teens and elders are normally limited to level 3 careers, so that would be your "clamp." You'd probably have to make a few intermediate levels too, to get to level 10 for adults.
I think I'd take a page from the Eco Guru career and have them go to work one day a week, probably Friday or Saturday evening, to simulate the infrequency of the fights. I guess you could use the Chance cards to simulate the win/loss chance.
Here's a link if you'd like to try:
http://modthesims.info/wiki.php?title=Tutorials:Career_Tutorials_Custom_CareersOtherwise, it would be a big help to whomever makes this for you if you'd write out the levels, the pay, the car, any custom rewards, etc.
No, I'm not volunteering!