One playing in poorish drama, humdrum ultimately (3)
I believe the answer is:
ham
'one playing' is the definition.
(thesaurus)
'poorish drama humdrum ultimately' is the wordplay.
'ultimately' suggests the final letters.
The final letters of 'poorish drama humdrum' are 'HAM'.
'in' is the link.
(Other definitions for ham that I've seen before include "Dried pig thigh" , "Succulent meat or extravagant actor" , "Meat served in sandwiches" , "Pork leg" , "Meat from a pig" .)