The men aged 37 and 41 in the field off Park Road in Dewsbury when they heard bangs and saw torches in the distance at 9.50pm last night
They walked in that direction when a group of men emerged from bushes.
The 41-year-old was hit, but managed to run away. The gang then knocked his friend to the ground and assaulted him.
His camouflage rucksack and a green bag containing a shovel and a garden fork were stolen.
The victim suffered swelling to his face along with bruises and grazes.
He told police he was attacked by a gang of around 30 Asian men aged between 16 and 30. All had their faces covered.
