A Christchurch man caught masturbating at a teenage girls' softball game has been sentenced to 12 months intensive supervision.

Martin Allen Graham appeared in the Christchurch District Court today on charges of committing an indecent act and possession of cannabis.

Graham had been smoking cannabis when he turned up to a softball game in March at Cowles Stadium.

He watched the girls playing while masturbating for around five minutes until he was interrupted by a concerned member of the public.

He ran off, but was caught by police, who found a very small of cannabis in his possession.