Guy upset about crazy fool's study of mysterious visitors (7)
I believe the answer is:
ufology
'study of mysterious visitors' is the definition.
'ufology' can be an answer for 'study' (I have seen 'Study of exotica' mean 'ufology' so perhaps 'study' could also mean 'ufology'). I'm not certain of the 'of mysterious visitors' bit.
'guy upset about crazy fool's' is the wordplay.
'upset' is an anagram indicator.
'about' means one lot of letters goes inside another.
'crazy' is an anagram indicator.
'guy' is an anagram of 'ugy'.
'fool' with letters rearranged gives 'folo'.
'ugy' placed around 'folo' is 'UFOLOGY'.
Can you help me to learn more?
(Other definitions for ufology that I've seen before include "Study of weird things in sky" , "Pseudoscience" , "New world for the study of flying saucers" , "Study of mysterious objects" , "Study of (supposedly) alien craft" .)