In play, an act is very bad indeed (7)
I believe the answer is:
satanic
'bad indeed' is the definition.
'satanic' can be an answer for 'bad' (I've seen this before). I'm not sure about the 'indeed' bit.
'in play an act is' is the wordplay.
'in play' indicates anagramming the letters (letters play around).
'an'+'act'+'is'='anactis'
'anactis' with letters rearranged gives 'SATANIC'.
'very' acts as a link.
Can you help me to learn more?
(Other definitions for satanic that I've seen before include "Nick's" , "Devilish (as Blake's 18)" , "Diabolical" , "Like hell it is" , "wicked" .)