Beat time, hard and over-hasty (6)
I believe the answer is:
thrash
'beat' is the definition.
(I know that thrash is a more specific form of beat)
'time hard and over-hasty' is the wordplay.
'time' becomes 't' (abbreviation).
'hard' becomes 'h' (abbreviation used in pencil classifications).
'and' says to put letters next to each other.
'over-hasty' becomes 'rash' (I've seen this before).
't'+'h'+'rash'='THRASH'
(Other definitions for thrash that I've seen before include "Soundly defeat; party" , "Beat thoroughly or make wild movements" , "tan" , "Beat; party (colloq.)" , "Punish" .)