Second whiskey! I'm having to crawl! (4)
I believe the answer is:
swim
'to crawl' is the definition.
(thesaurus)
'second whiskey i'm' is the wordplay.
'second' becomes 's' (common abbreviation).
'whiskey' becomes 'W' (alpha bravo charlie delta ...).
'i'm' becomes 'im' ().
's'+'w'+'im'='SWIM'
'having' acts as a link.
(Other definitions for swim that I've seen before include "Crawl, e.g." , "Do the dog paddle, perhaps" , "To be in the .... is knowing what is going on" , "Bathe" , "At . . . . Two Birds by Flann O'Brien" .)