Not quite - even though the heavier ball would require more force to get it to the same velocity, it would still follow the same path as the lighter ball. Mass would have no effect on speed, direction, or the path of the ball under any non-relativistic circumstances, regardless of how fast the inertial frame of reference (the passer) was moving - mass would only effect the required force to get it [ito[/i that speed and in that direction.

That's quite impressive! I get bored after about 22

Not true, I actually changed my wording so that that would not be the case - "mass would only effect the required force to get it to that speed and in that direction".

Just because I didn't make clear what was applying the force doesn't change the fact I didn't exclude air resistance.

Can you work out the path of the ball then (other forces acting on it like air resistance and gravity) using trigonometry then?

i.e. If a static player passes a ball backwards at a 45degree angle at 10m/s, then using trigonometry it's velocity in a directly backwards direction is 7m/s.

If then a second player makes the exact same pass but is running forwards at 10m/s, then it would travel forward at 3m/s? (10m/s forwards - 7m/s backwards = 3m/s forwards).

Using Newtonian physics you can, yes.

To your example, then yes, the ball would travel forward at approximately 3m/s. At such slow speeds air resistance wouldn't have too much of an effect anyway.