Arab blocking American subject running race (8)
I believe the answer is:
marathon
'race' is the definition.
(marathon is a kind of race)
'arab blocking american subject running' is the wordplay.
'arab' becomes 'ar' (abbreviation in Chambers).
'blocking' is an insertion indicator.
'american subject' becomes 'math' (math is a kind of subject. I am not sure about the 'american' bit.**).
'running' becomes 'on' (I've seen this in other clues).
'ar' going inside 'math' is 'marath'.
'marath'+'on'='MARATHON'
Can you help me to learn more?
(Other definitions for marathon that I've seen before include "Long and arduous" , "Footrace of 26 miles 385 yards" , "Pheidippides' starting point" , "Olympic event" , "Race of about 26 miles" .)