Thug knocking over John and Henry, one with crew cut (8)
I believe the answer is:
hooligan
'thug' is the definition.
(I've seen this before)
'knocking over john and henry one with crew cut' is the wordplay.
I cannot really see how this works, but
'over' could be 'o' (cricket abbreviation) and 'o' is found in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is located in the answer.
'henry' could be 'h' (symbol for the unit of electrical inductance) and 'h' is found within the answer.
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
The remaining letters 'olga' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for hooligan that I've seen before include "Yobbo" , "A young ruffian" , "Ruffian, yob" , "Rough, lawless person" , "Antisocial rough" .)