Intense struggle among rodents (3,4)
I believe the answer is:
rat race
'intense struggle' is the definition.
'rat race' can be an answer for 'struggle' (I have seen 'Daily struggle ' mean 'rat race' so perhaps 'struggle' could also mean 'rat race'). I'm not sure about the 'intense' bit.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for rat race that I've seen before include "day-to-day struggle" , "Rare cat (anag.)" , "struggle for position" , "may be won by a whisker?" , "Scramble to succeed" .)