Signed up in preparation for a match? (7)
I believe the answer is:
engaged
'signed' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for engaged that I've seen before include "being committed to union" , "Bethrothed" , "Spoken for" , "Busy; employed" , "Fully occupied" .)