When I first heard the phrase en pelotas I had to ask what it meant. My informant was then unable to explain to me what it had to do with the object with which games are played nor with the sport often associated with the Basque region. Recently on seeing a headline where a performer complained that people kept asking her to pose en pelotas I started to search for more enlightenment.
In the DLE I discover that this is a separate derivation of pelota
dejar a alguien en pelota, o en pelotas
- locs. verbs. coloqs. Quitarle o robarle todo lo que tiene.
en pelota, o en pelotas
- locs. advs. coloqs. Desnudo, en cueros. U. t. c. locs. adjs.
That obiously makes more sense since I know that pelo is skin. But where does the suffix fit in? Further search reveals
1. suf. U. para formar aumentativos y despectivos a partir de adjetivos y nombres. Bobote, grandote, angelote, marquesota.
Is this usage really despectivo and since it is a masculine noun why is it not pelote rather than pelota?
Incidentally I do not recommend an internet search for the phrase en pelotas if you are working in a public place.