On purpose, making motto (6)
I believe the answer is:
legend
'motto' is the definition.
(I've seen this before)
'on purpose' is the wordplay.
'on' becomes 'leg' (cricket term, fielding positions).
'purpose' becomes 'end' (I've seen this before).
'leg'+'end'='LEGEND'
'making' acts as a link.
(Other definitions for legend that I've seen before include "Story about mytical beings" , "Celebrity" , "Very famous member's death" , "Story from long ago" , "Inscription; myth" .)