Difficult time with Yankee in boxing venue (6)
I believe the answer is:
trying
'difficult' is the definition.
(similar in meaning)
'time with yankee in boxing venue' is the wordplay.
'time' becomes 't' (abbreviation).
'with' says to put letters next to each other.
'yankee' becomes 'y' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' indicates putting letters inside.
'boxing venue' becomes 'ring' (boxing ring).
'y' inserted inside 'ring' is 'rying'.
't'+'rying'='TRYING'
(Other definitions for trying that I've seen before include "Attempting or irritating" , "Causing strain, annoying" , "Working in a court can be" , "Exasperating" , "Difficult - annoying" .)