Nobunaga succeeded at the Battle of Okehazama due to he was able to trap the Imagawa and the crush them in a surprise attack. David D. Neilson's thesis Society at War goes into great detail on this. Neilson (pp. 80-81).
"It soon became clear that the Imagawa would pass through an area where there were several riverside villages under the leadership of a village headman named Tozaemon, a man with whom Maeno Shoemon and Hachisuka Koroku were acquainted. Seeing this as the opportunity they needed to halt the progress of the Imagawa army that they had been waiting for, Maeno and Hachisuka set their plan in motion. Bringing them a large amount of carefully chosen foods and sake, they and some of their men joined a group of villagers led by the aforementioned Tozaemon and some Shinto and Buddhist priests, and went out to the road to wait for Imagawa Yoshimoto to pass by. They were planning to offer the food to him as a gift celebrating the auspicious beginning of his campaign against Nobunaga and secure his favor.
They waited on their hands and knees in the dirt on the side of the road with their gifts laid out on white cloths. It was so hot that those who were waiting later said that they became dizzy from the heat. It was no small gesture-and no small risk for peasants to approach someone like Imagawa Yoshimoto and the Imagawa outrider who initially encountered them told them to disperse or be cut down. They were persistent however, and after the outrider returned to tell Imagawa Yoshimoto of the peasant's wish to offer him their congratulations, Hachisuka Koroku, who was secreted within the group, had the villagers move to a place further down the road to a place which was shady and therefore more inviting during the heat of the day. The trees and hills father down the road also provided much needed cover for the approach of the Oda army which was already riding out from Kiyosu to lay in wait among the nearby hills and villages. Onikuro who Maeno and Hachisuka had been ordered to report to once they had Yoshimoto's location, had been sent out ahead of the main Oda force. He took their report and rode back to relay this critical piece of intelligence information directly to Nobunaga."
The gift giving scene is played out really well in the movie Fuunji Oda Nobunaga (1959). The Men of the Fields did everything they could to make sure the trap worked or Nobunaga would not have been successful at at. The weather played a key role and the Imagawa army must have been exhausted from the intense heat. The gifts of food and drink along the shade of the trees provided much relief to the Imagawa army. Yoshimoto took the bait and the rest was history. Happy Battle of Okehazama Day!
Okehazama no tame!