Fire investigator Craig Bain had no doubt that the fire that destroyed a corrugated iron shed at Te Rarawa Rugby Club's home field at Ahipara on Sunday was deliberately lit after he examined the remains.
The shed was not connected to electricity, he said, and the contents would not have spontaneously combusted.
police from Kaitaia were due to examine the scene yesterday afternoon.
The fire destroyed the shed and contents, including a truck load of ti-tree firewood, on Sunday afternoon, the Ahipara and Kaitaia fire brigades responding just after 2pm.
There was nothing the crews could do to save the shed, but they pulled sheets of iron away to open it up for the hoses, preventing damage to another small shed on one side and the main clubrooms building, immediately adjacent on the other.
Kaitaia's deputy Chief Fire Officer Ross Beddows said the shed had not had electricity, which eliminated one major potential explanation, but the word at the scene was that children had been seen running shortly before the alarm was raised.