Blocked, having rushed to claim summit (7)
I believe the answer is:
stopped
'blocked' is the definition.
('stop' can be a synonym of 'block')
'rushed to claim summit' is the wordplay.
'rushed' becomes 'sped' ('speed' can be a synonym of 'rush').
'to claim' means one lot of letters goes inside another (inserted letters are claimed or taken in).
'summit' becomes 'top' (synonyms).
'sped' enclosing 'top' is 'STOPPED'.
'having' acts as a link.
(Other definitions for stopped that I've seen before include "gave up" , "What Terminator did" , "Ceased, ended" , "Prevented" .)