take on
accept sth (a challenge)
try sth out
do sth for the first time
referee
give up
stop trying sth
drop out of
quit being part of sth
opponent
pick sth up
learn sth
teammate
let sb down
make sb disappointed
burn (sth) off
get rid of (fat or calories)
referee
Cheer sb on
shout loudly to encourage sb
go in for
take part in sth
put sb off
discourage sb