Why did Dhoni shave his head immediately after winning World Cup 2011?

When Dhoni posed with the world cup trophy the day after getting India to victory with a six with the Gateway of India as the backdrop in 2011, everyone was surprised to see the captain sporting a bald look. He had apparently shaved off his hair in the hotel the previous night. This was apparently part of a sankalpa (promise) made to a deity near his hometown in Ranchi. A priest had apparently given instructions to shave his head between 2:45 am to 3:00 am. Dhoni adhered to this timeline. The hair was subsequently offered to the Tirupati Tirumala Devasthanam located in Andhra Pradesh. 

Dhoni had won the man of the match trophy in the finals of the 2011 ICC Cricket World Cup for his unbeaten 91 that had come as a timely intervention when the match was evenly poised against finalists Sri Lanka. 

As per Hinduism it is believed that this act is a means of getting closer to god. The act of tonsuring one’s hair is symbolic of letting go of one's vanity and arrogance.