"He went to tackle him and got his finger caught in the spoke - he lost the finger and a tooth in the process amongst other injuries," she said.
The alleged thief then crashed the dirt bike and fled the scene, running through the river, and was tracked down shortly after by police dogs at Henley Lake.
Masterton man Jason Dean Hart, 17, appeared in Masterton District Court yesterday charged with unlawfully taking a motor vehicle, and Ms Watson said other charges were likely after further inquiries were made.
Hart was remanded until October 8 without plea, released on bail with a 24-hour curfew.
A hospital spokesperson said late yesterday that the injured man had come out of surgery and was in a satisfactory condition.