Clue: Mediocre performer wanting praise, forgetting line after overacting (9)
Answer: HAMFATTER
Explanation: Definition: Mediocre performer
A charade of HAM ('overacting' – but the word is probably derived from hamfatter) plus F[l]ATTER ('praise') minus the L ('forgetting line'). 'After' gives the order of the particles, and 'wanting' is a link word.