no prep random encounter, they each get 1 weapon, Bats gets his batarangs, Natasha Get Her Widows sting, and Lady Shiva gets a sword who takes it
Black Widow has the Red Room version of the Super Soldier Serum. She literally spent an entire day walking on her hands showing both her peak human strength and superhuman stamina. Her Widow's Sting is the best weapon of the bunch and she is the most experienced of the three. If she performs per her stats, she should be able to take Bats solo.
Okay well Shiva doesn't solo, but her and Black Widow together tip this in their favor. Bruce has either tied or bested Shiva on more than one occasion and she's a bloodlusted relentless fighter whereas he is a controlled, as not to kill fighter. The team wins unless Bats gets some help or he's also out for blood.