Maybe like Sumo, two bad losses and must retire? It has to be hard to let go of something when you have had so much success at it.
In sumo it really depends on rank. Allow me to explain for those who are not familiar.
Before I get started: the real situation is actually more complex, but allow me to cut some non-essential corners for clarity.
There are 6 tournaments in a year, each one taking 15 days. All top tier fighters fight every day. If you win more than you lose, you go up. If you lose more than you win, you go down in the rankings. Forget about injury or whatever because noone cares. If you break you leg on day 1 or have a burst appendix, that counts as 15 losses. If you need long rehad and miss the next tournament, that's another 15 losses. Sumo knows no mercy.
The closer you get to the top, the harder it becomes to get promoted, but the top 2 levels have some leeway to prevent instant demotion for a majority of losses.
The second to highest level: champion (Ozeki) has some protections, but once you fall back, you either retire before actually being demoted (if you are old-ish) or you just keep on going if you are younger.
Young people can usually stay competitive near the top, while old people tend to fall all the way down, due to bodies that are basically destroyed. This is why they retire. Not because they have to. They know that they don't have a hope of getting back to that leel, and the shame of falling all the way down is just too much.
Once someone reaches the exalted rank of grand champion (Yokozuna. this is rare) he cannot be demoted. But this is small mercy because he is not expected to ever get a majority of losses in a tournament. Ever less than double digit results (10 win 5 loss) is frowned upon.
If a yokozuna ever faces the possibility of majority of losses, he either bails out on medical reasons (sometimes referred to as yokozunitis) or he retires before that happens. This depends on whether there is hope for the future or not. If his health and body are shot, it is likely a retirement. If it is only temporary (e.g. dislocation or inflammation) it is likely the latter.
So there is no rule to make you retire unless you are yokozuna. But in that case it won't take 2 failed tournaments. 1 should suffice.
From Ozeki to all the way down, retirement is purely at the choice of the fighter, but this is where shame and pride kick in. No Ozeki keeps on going until he has been demoted to entry levels and has become a human punch bag.