Hands up for success in school sport (4,5)
I believe the answer is:
high fives
'hands up for success' is the definition.
(gesture of raised hands celebrating success)
'school sport' is the wordplay.
'school' becomes 'high school' (high is a kind of school).
'sport' becomes 'fives' (fives is a kind of sport).
'high'+'fives'='HIGH FIVES'
'in' is the link.
(Other definitions for high fives that I've seen before include "Greetings from America" , "Heartily welcomes" .)