When John practised karate as a hobby

[Bassim]

I am wondering if my sentences are grammatically correct.

When John practised karate as a hobby he could never have imagined that one day he would have a good use of it in the street. One night as he was attacked by two muggers, he reacted instinctively and knocked them both down.

 

[Tarheel]

I would say:

have good use for it

 

[GoesStation]

Make good use of it would be more natural.

 

[Tdol]

Or put it to good use.