Periodically, gantry behind sports ground may be so (5)
I believe the answer is:
peaty
'ground may be so' is the definition.
I can't judge whether this defines the answer.
'periodically gantry behind sports' is the wordplay.
'periodically' indicates alternate letters (letters must be selected 'every so often').
'behind' means one lot of letters go next to another.
'sports' becomes 'pe' (Physical Education).
The alternating letters of 'gantry' are 'aty'.
'aty' put after 'pe' is 'PEATY'.
Can you help me to learn more?
(Another definition for peaty that I've seen is " Like some whiskies".)