Power behind punt, say, that's in beastly kicker's leg (7)
I believe the answer is:
pastern
'punt say that's in beastly kicker's leg' is the definition.
I can't tell whether this definition defines the answer.
'power behind' is the wordplay.
'power' becomes 'p' (symbol in physics).
'behind' becomes 'astern' (at the back or behind of a ship).
'p'+'astern'='PASTERN'
Can you help me to learn more?
(Other definitions for pastern that I've seen before include "Wrongly-defined part of horse" , "Word Johnson misdefined" , "Part of horse's foot" , "'The knee of an horse' (Johnson)" , "part of Arab's leg" .)