One’s exercise with ball shows restraint (9)

'restraint' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

'one's exercise with ball' is the wordplay.
'one's' becomes 'I'm' ('one is' is a formal way of saying 'I am').
'exercise' becomes 'pe' (Physical Education).
'with' means one lot of letters go next to another.
'ball' becomes 'dance' (ball can mean an event for dancing).
'im'+'pe'+'dance'='IMPEDANCE'

'shows' is the link.

Can you help me to learn more?