My team is 17 games into the season and all of my hitters are still listed at 100%.  At least half a dozen of them (although not my catchers, I know they need occasional rest so I platoon there) have started every game.

Will they eventually get fatigued if I don't rest them?  At what point in the season does that usually happen?  Is it related to their health and durability?  How often (if ever) do you give players in your starting eight a day off?

Yes. 
Depends on the their durabilty.
Yes.
Depends on their durability.

I think it also depends on what positions they are playing.  Is that correct?

If a guy has durability over, say, 88-90, he can probably play every game or almost every game without fatigue. Most guys can't. If you keep playing everyone every day, you should start to see some of the lower durability guys drop below 100% around the time of the draft. After the All Star break, your guys in the mid70s to low 80s will start having fatigue problems too. I've read that the position does matter, but it doesn't make a huge difference.

If you want to avoid d guys dropping below 100, you'll need to give them occasionally days off. I like to have a couple utility guys on my roster, one who can play 2B, SS, and CF, and one who can play 1B, 3B, LF, or RF. there are a lot of scheduled off days at the beginning of the season, so I don't do much substitution until about game 40 or so. But after that I rotate my utility guys through the lineup, concentrating on giving more off days to guys with lower durability.

On some teams I don't do such a great job of this, and I see fatigue setting in around the 100th game. Once a guy drops to 99, you usually have to rest him a couple games. If you rest him one game he'll be back at 100, but then he'll drop again after a game or two. It's not the end of the world to play a guy at 98 or 99, but I've read that playing guys when they drop lower than that can increase injury risk.

Posted by arcticlegend on 8/11/2015 9:48:00 PM (view original):
If a guy has durability over, say, 88-90, he can probably play every game or almost every game without fatigue. Most guys can't. If you keep playing everyone every day, you should start to see some of the lower durability guys drop below 100% around the time of the draft. After the All Star break, your guys in the mid70s to low 80s will start having fatigue problems too. I've read that the position does matter, but it doesn't make a huge difference.

If you want to avoid d guys dropping below 100, you'll need to give them occasionally days off. I like to have a couple utility guys on my roster, one who can play 2B, SS, and CF, and one who can play 1B, 3B, LF, or RF. there are a lot of scheduled off days at the beginning of the season, so I don't do much substitution until about game 40 or so. But after that I rotate my utility guys through the lineup, concentrating on giving more off days to guys with lower durability.

On some teams I don't do such a great job of this, and I see fatigue setting in around the 100th game. Once a guy drops to 99, you usually have to rest him a couple games. If you rest him one game he'll be back at 100, but then he'll drop again after a game or two. It's not the end of the world to play a guy at 98 or 99, but I've read that playing guys when they drop lower than that can increase injury risk.

Agree with all this, except that I do think that position matters a lot if the position is catcher.

You can also manage fatigue by paying attention to the schedule. When you're playing the other league — teams you are not competing against for playoffs — rest a few of your lower-DUR guys. You want your best team on the field for divisional games first, and then for league games. All games count, but a win over a playoff rival is twice as helpful as one against the other league or a .380 team.

If you don't want to micro manage every game once a player gets to 99% platoon him  and his fatigue will stay at or near 100..

Avoid playing your  offensive starting players in spring training, they will last longer into the regular season..

Or you can just be really lazy like me and set them at 99% auto rest.

I use the loose rule of Durability = % of 162 games that a guy can start and remain near 100%.

A guy with 80 Dur can start about 130 games and remain at/near 100%,  It's close, anyway.

But you have to try to rest them appropriately.  So I try to rest a guy with 80 Dur. for 3 or 4 games out of every 20.  

If he's 70 Dur, then he gets 5 or 6 game off....out of every 20.  

I think there are weird factors at play, as well.  For me a guy who starts at 3 positions fatigues more quickly than a guy who just starts at 1.  And a 1B, of course, fatigues a bit more slowly than a CF.

That's too much rest. Hardball Dynasty – Fantasy Baseball Sim Games - Player Profile: Kevin Ryu can easily play 145.   You'd be playing him about 120.  

Posted by moethedog on 8/13/2015 9:04:00 PM (view original):
I use the loose rule of Durability = % of 162 games that a guy can start and remain near 100%.

A guy with 80 Dur can start about 130 games and remain at/near 100%,  It's close, anyway.

But you have to try to rest them appropriately.  So I try to rest a guy with 80 Dur. for 3 or 4 games out of every 20.  

If he's 70 Dur, then he gets 5 or 6 game off....out of every 20.  

I think there are weird factors at play, as well.  For me a guy who starts at 3 positions fatigues more quickly than a guy who just starts at 1.  And a 1B, of course, fatigues a bit more slowly than a CF.

I agree with Mike. This is way too conservative. I've found that guys with 90+ DUR can pretty much play every game. You definitely don't need to rest them 10% of the time. And a guy at 80 could probably do 150 if you manage his days off well.

Maybe it might be better if you use the percentage formula with the whole season, including off days. I haven't counted recently, but I think you get about 12-13 off days in a season total. So the total number of days is closer to 175. Lookong at it that way, a guy with 90 DUR could play about 90% of 175 days, or about 158 games, without fatigue. And a guy with 80 DUR could play 140.

It's still a little conservative, but if you're looking for a formula, the numbers are a little cleaner and more accurate.

Last season I had a 95 DUR play all games in left field/first base, an 89 DUR play 156 at DH, an 84 DUR play 155 games at first base/DH, a 77 DUR play 145 games at SS. None were defensive replacements and two of them had two pinch-hits apiece for the whole year.

If I go by the durability as a percentage benchmark, I'd have sacrificed roughly 60 games with just those four players alone. While I see your point about it being a "loose" guideline, I can't imagine following it at all. Players play when they're at 100 percent. If they're not, they get a day. Simple as that.

You'll get a feel for it soon enough.   I'd run the 90 dur into the ground until fatigue hits, play the 80 dur about 11 of 12 games until fatigue hit and give the 70 guys a game off every 8-9 games. 

DH and 1B clearly are different animals.  Did those guys stay at 100%.  That was the point I made.  Guys would stay at 99-100%.  I've had 90 Dur. guys who could not start every game at 100%.  They hit 99% half way though the season.  Mike, I was talking about starts, not games played.  Ryu started 135 games in season 35 and 120 in 36.