Great fights erupting — an unwelcome experience in the theatre (5,6)
I believe the answer is:
stage fright
'an unwelcome experience in the theatre' is the definition.
I can't tell whether this definition defines the answer.
'great fights erupting' is the wordplay.
'erupting' indicates anagramming the letters.
'great'+'fights'='greatfights'
'greatfights' is an anagram of 'STAGE-FRIGHT'.
Can you help me to learn more?
(Other definitions for stage fright that I've seen before include "Pre-performance nerves" , "problem for players" , "Panic experienced by performer" , "Actor's fear" , "Dramatic nerves" .)