Cassette re-established legal precedent (4,4)
I believe the answer is:
test case
'legal precedent' is the definition.
'test case' can be an answer for 'precedent' (I've seen this before). I'm unsure of the 'legal' bit.
'cassette re-established' is the wordplay.
're-established' is an anagram indicator.
'cassette' anagrammed gives 'TEST CASE'.
Can you help me to learn more?
(Other definitions for test case that I've seen before include "Precedent-setting trial" , "Lawsuit whose decision will form precedent" , "Court precedent" , "Trial to establish precedent" , "Legal action serving as a precedent" .)