The term is 'excessie movement behind".
Now reality is all saddles move a BIT behind. … is it a GREAT fit with some movement behind? no. would i pass it over? Depends on budget and what we’re fitting against…
You need to think of saddle fitting as a set of check boxes… how many need to be ticked off as 'good"?? Well obviously we aim for ALL. but if i have 9 out of 10 boxes?? and we’re in the clients budget and the horse is happy in the saddle? HELL YES i’m happy with that fit! there are different levels. We have OK, decent, good, great and god i can’t believe how wonderful that is!.
Saddles change as horses change. My horse had 3 months of this winter- voila his saddle’s rocking a bit… WHY? he’s changed shape. Tweaked flocking a bit and rocking is down to nothing. Have had clients who had saddles who fit REALLY well but the horse REALLY hungered down behind- doubled with ‘regular’ billets- voila too much movement behind. Changed to a V billet behind and the excessive movement is reduced.
Also- movement behindo nthe lunge/in hand is NOT a sign of a bad saddle fit-… don’t worry about that- see what it does IN thes addle. Also i’ve seen certain riders make a saddle move more behind then others… some of them making it move ALOT… so much plays into it.
MY advice?? GET A FITTER. it’s less work- less money and less stress in the end.