Excited handclap welcomes United - ground expecting explosive start! (6,3)
I believe the answer is:
launch pad
'ground expecting explosive start' is the definition.
(where a rocket launches)
'excited handclap welcomes united' is the wordplay.
'excited' indicates an anagram.
'welcomes' means one lot of letters goes inside another (in sense of 'invites in').
'united' becomes 'U' (abbreviation).
'handclap' is an anagram of 'lanchpad'.
'lanchpad' placed around 'u' is 'LAUNCH PAD'.
(Other definitions for launch pad that I've seen before include "Good place to begin" , "that's a good start" , "that can kick-start career" , "platform" , "explorer's starting place" .)