Every principal to begin with studied dancing and acted as understudy (9)
I believe the answer is:
deputised
'acted as understudy' is the definition.
I can't judge whether this defines the answer.
'every principal to begin with studied dancing' is the wordplay.
'to begin with' suggests taking the first letters.
'dancing' is an anagram indicator.
The initial letters of 'every principal' is 'ep'.
'ep'+'studied'='epstudied'
'epstudied' is an anagram of 'DEPUTISED'.
'and' is the link.
Can you help me to learn more?
(Another definition for deputised that I've seen is " Stood in (for)".)