Hi Gaz. I had a lad (u11) who did the same. What I did was in a training game. Put some flat cones around an area I wanted him to stay in, this worked for me. Obviously it doesn’t help when you need him to cover across the back but he started to understand about not chasing the ball.

Young players tend to chase the balL because they want the ball so it is normal. At this age I’d still not have players in set positions and play a few across 1 or 2 units . What positions does this player play out of interest? You could use constraints or pitch Markings. E.g if it’s a wide player they must stay in the wide area until they receive  the ball in the final third. Could even use rewards like if a goal comes after they receive the ball in a certain areas it’s worth double 

Young players tend to chase the balL because they want the ball so it is normal. At this age I’d still not have players in set positions and play a few across 1 or 2 units . What positions does this player play out of interest? You could use constraints or pitch Markings. E.g if it’s a wide player they must stay in the wide area until they receive  the ball in the final third. Could even use rewards like if a goal comes after they receive the ball in a certain areas it’s worth double