Singers regularly using ballet tops (5)
I believe the answer is:
altos
'singers' is the definition.
(alto is a kind of singer)
'regularly using ballet tops' is the wordplay.
'regularly using' indicates alternate letters.
'ballet'+'tops'='ballettops'
The alternating letters of 'ballettops' are 'ALTOS'.
(Other definitions for altos that I've seen before include "Lowest female singing voices" , "Females who sing in the lowest range" , "High male or low female voices" , "Singers" , "Choir members" .)