Persevere over each period before play starts (3-6)

I think it could be either:

Which length description are you looking for?:

3-6

pre-season

'period before play starts' is the definition.
(before a sporting season begins)

'persevere over each' is the wordplay.
'persevere' becomes 'press on' (to press on is to persevere).
'over' indicates putting letters inside.
'each' becomes 'ea'.
'presson' enclosing 'ea' is 'PRE-SEASON'.

Want a hint initially instead of a full solution? Install my app