"An educated guess, it could be a dropped cigarette, or possibly deliberately lit.
"There were no vehicles and the gate was locked - it's pretty suspicious.
"Unfortunately we do get quite a few of these type of calls around the Henley Lake area."
Red Star rugby club president Gavin Sullivan said they were not allowed to irrigate the area because of water restrictions.
"It's just one more thing we could do without," he said.
The fire potentially affects the season for junior rugby, when there might be three teams practising on the ground.
"We can't do anything about it [not irrigating] at the moment," he said.
Wairarapa Bush junior rugby chairman Doug Bracewell went to see the damage yesterday and said it was "quite bad".
He joked that perhaps the meteorite, which had made national news yesterday, had come to rest in Masterton.
"With a bit of water, it could come away again with a bit of resowing."
He said games did not start until the first week of May, but training would begin sooner.