The Spanish father in Rome loses the head leading strike and, for Union reasons, splits with girlfriend (6)
I believe the answer is:
elopes
'rome loses the head leading strike and for union reasons splits with girlfriend' is the definition.
I can't tell whether this definition defines the answer.
'the spanish father' is the wordplay.
'the spanish' becomes 'el'.
'father' becomes 'opes' (I can't explain this - if you can you should give a lot more credence to this answer).
'el'+'opes'='ELOPES'
'in' acts as a link.
Can you help me to learn more?
(Another definition for elopes that I've seen is " Runs away to get married".)