I have a player, his stamina is 75 and his health is 98. How low can i let his % go without risking injury. And what do people usually let the % get to before they bench their players?

I try not to let my guys get under 98% unless/until it's late in the season and I need to push them if I'm fighting for a playoff spot.

It depends on the situation but I try to never go below 98% either. I tend to have a very deep bench and not a lot of stars. In other words I am more likely to have a 77 starter with a 74 backup, then a 82 starter with a 68 backup. So keeping guys fresh usually works for me. My goal is to have them all at 100% when the playoffs start. In my opinion the whole season is an extended spring training and a few losses during the season are OK if it gives you a better chance in the playoffs, assuming you are good enough to get there. But if you are struggling to get there you have to play your studs and take some risks.

Same as dean, I build my teams to act as teams, and have good benches.  I usually save ABs early in the year by having a utility guy play almost every day all over the diamond.  I sit guys when they dip below 100%.  I have seen plenty of owners playing guys down to 80% many times, but have never done it.

Depends on the situation.  For a playoff caliber team I want my guys as close to 100% as possible when the playoffs come.  For an also ran team I normally will keep the starters in toward the end of the year and they can get a little fatigued that way.  In either case I almost never let a guy play below 90%.

My guys don't play less than 100%.  I do nearly the same as ranger:  I usually rest all my starters once every 10 games.  Can do so with a 4th OF/3B/2B, a utility SS, a backup C and a2nd 1B, where I sometimes platoon.

I tend to treat (no where near the seasons some guys on the forum have in experience) the stamina rating for position players as a percentage of games they can play out over 162 games.  I have guys with 90's plus stamina make it 150 + / - games a season.  A guy with a 75 has me looking at 120 to 130 games tops.  Last season I was playing against teams at the end of the year with guys in the 70's for stamina, to me (again little empirical evidence) thats just a huge injury risk.