Saint who had to look out for trouble starting (5)
I believe the answer is:
peter
'saint who had to look' is the definition.
'Peter' can be an answer for 'saint' (I've seen this before). I am not certain of the rest of the definition.
'out for trouble starting' is the wordplay.
'out' indicates putting letters inside.
'for' becomes 'peer' (I am not sure about this - if you are sure you should believe this answer much more).
'starting' indicates taking the first letters.
The initial letter of 'trouble' is 't'.
'peer' going around 't' is 'PETER'.
Can you help me to learn more?
(Other definitions for peter that I've seen before include "Blue -, ship's flag" , "Cephas" , "One of Jesus' disciples" , "Early Pope" , "Play high card before low" .)