BRANDISHING a replica handgun as he chased four teenagers up the street, Leigh William Santillan suddenly stopped to help one of the teens who had collapsed with an asthma attack.

The four teens aged between 14 and 17 were walking past Santillan's Rockville home late on Christmas Eve when one of the group kicked and damaged the letter box, Toowoomba District Court heard.

Santillan had gone outside to challenge the group, telling them he was a member of an outlaw motorcycle gang and that they didn't know who they were dealing with.

When the group returned verbal abuse, Santillan went back inside but soon returned with a replica handgun and the four had run off, Crown prosecutor Noel Needham said.

One of the teenagers suffered an asthma attack and stopped at a bus shelter where Santillan arrived and pointed the replica gun at the boy's head telling him to lie on the ground.

When the boy's mate said the teen was having an asthma attack, Santillan calmed down.

The affected boy told Santillan where he lived and asked him to retrieve a puffer spray for him.

Mr Needham said Santillan instead ran to his home and gathered his own puffer which he gave to boy who soon recovered.

Arrested the next day, Santillan had been held in custody since until he pleaded guilty yesterday to a charge of going armed to cause fear.

His barrister Steve Kissick said his client knew he had an anger problem and had over-reacted that night.

Since being in custody Santillan had been diagnosed with an anger disorder for which he was now medicated, Mr Kissick said.

Judge Richard Jones declared 143 days custody as time already served and sentenced Santillan to nine months jail but ordered he be released immediately on parole.