Hey guys, whats the difference in these two stats, does Ball carrying affect how a players speed is changed when he has the ball and avoid fumble just make a difference for chance that he fumbles or what..?

Short answer, yes. I’m sure I’m not the expert to explain it properly, but my understanding and experience seems to show that avoid fumble is exactly that, just how likely that player is to lose their grip on the pigskin. Ball carrying would seem to be how well that player runs with the ball, as I have players with good scores in this skill outperform otherwise faster players in yards per carry. I’m not sure it it is really all that important compared to avoid fumble and speed when ranking running backs, but it could be a useful tie breaker beyond those key skills.

RBs with 100 avoid fumble will still fumble. I've heard in 4.6 that ball carry has increased importance.

I know it doesn’t completely eliminate fumbles, but I had a rb that was fast, good ball carry and receiving skills…big plays left and right, but a avoid fumble below 30 and seemed to lose one every game. Nothing is absolute in this game, but losing the ball is pretty predictable with a low avoid fumble.

A 100 AF back had 20 touches a game for 2400 total yards. He fumbled only twice. Where a zero AF back had near 16 touches a game for 1300 yards. This was an older code but still fumbled 17 times. I like to think he’d fumble more in the current version.

The key here is how you abuse the back. Neither of those guys really were. Conditioning kicks in and a lot of higher than normal numbers happen here all throughout the game. Not just with fumbles. Strip is lined up against AF but something will happen within those two ranges mentioned above if you don’t tire the back out before he can get his wind back

That boom or bust back I mentioned was primarily my #2 rb because I didn’t trust over use…maybe 10-15 touches a game…still always good for one fumble in there.

RB:
ball carry has more of an effect on fumbles by any player possesing the ball. Forgot where I read it, to lazy to look up a link, but pretty sure it was something setherick mentioned when he posted (edit: his) 4.5 weights. I try not to go below 50 for either if it's a RB.
Route running has more of an importance than pass catching for RB's (again - setherick data somewhere), though I have seen so very many exceptions to the rule via game experience.
If a RB cannot catch, they cannot catch has been my game play experience. Same for WR. I've certainly seen low rated players in pass catch and route do exceptionally well over their careers at the RB position.

It is not abnormal to see a player perform beyond the sub attributes in regards to catches, especially at RB.
Right player, right position, right play. Overrides matter.

EDIT: Every failed WR is a RB waiting to happen ;)