Ballroom dance seen, opt out! (3-4)
I believe the answer is:
one-step
'ballroom dance' is the definition.
(one-step is a kind of ballroom dance)
'seen opt out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'seen'+'opt'='seenopt'
'seenopt' anagrammed gives 'ONE-STEP'.
(Other definitions for one-step that I've seen before include "Kind of foxtrot" , "Foxtrot's precursor" , "(Very short?) ballroom dance" , "Style of foxtrot" , "Vigorous dance" .)