Hairbelly was a weasel slave driver in Slagar the Cruel's band. He was assigned to be the balancer in the pretend circus the slave drivers acted as when they infiltrated Redwall Abbey.
Hairbelly complained about numerous things, including that the slave drivers are doing all of the hard work and being the balancer. Slagar then ran him through with his sword in front of the rest of the band to teach them a lesson and dumped Hairbelly's body outside in the churchyard.