Imagine you are somewhere in a playing field attached to a car park and your son's football is somewhere else in the playing field, so:
you (the speaker)----------------ball -----------car park
If your son is standing next to you or at any point on the line between you and the ball, you could say:
(i) 'Can you get the ball, please.' (son---->ball)
Why? Because:
'get' means make a movement towards something in order to pick it up.
If your son is at the ball but the ball is not in his hands, you could still say 'get' because your son has to make a movement towards it, ie reach down, to pick it up.
Depending on the context 'get' can also mean 'bring' (towards the speaker), so:
'get' means make a movement towards something in order to pick it up and bring somewhere.
(ii) 'Can you get me the ball, please.' (son---->ball ---->you)
(in which case 'fetch' is also possible)
or 'take' (away form the speaker), so:
'get' means make a movement towards something in order to pick it up and take somewhere.
(iii) 'Can you get the ball and take it to the car, please.' (son---->ball---->car park)
Combining those meanings:
'get' means to make a movement towards something in order to pick it up (or pick it up and bring or take somewhere)
You would only say 'bring' if you wanted your son to come back to you with the ball (and not the car park or elsewhere, away from you)* and your son:
(a) is beside the ball (in which case 'get' is also possible, as noted above); or
(b) has the ball in his hands (in which case, 'get' is not possible since there can be no movement towards the ball - it's already in your son's hands!)
So:
(iv) 'Can you get me/fetch the ball, please.' (son----->ball------->you)
(v) 'Can you get me/fetch/bring the ball, please.' (son->ball------>you) (note short arrow: the son is already beside the ball)
(vi) 'Can you bring the ball, please.' (son (carrying the ball)----->you)
(vii) 'Can you get the ball and take it to the car park.' (son----->ball----->car park)
* I'm simplifying the meaning of 'bring' by applying it to this context only; in other contexts 'bring' can mean to take to another place but I don't want to enter a lengthy discussion of the full meanings of bring/take (and come/go)