DISCLAIMER: I do not own the Avengers or the Justice League.

Batman stalked through the shadows in the engine room of the SHIELD helicarrier, having already seen the layout of the ship on some stolen blueprints. He was almost at the prison bay where Selina Kyle would be imprisoned. Catwoman had been beaten by a woman named Black Cat, and taken into custody by SHIELD, and Bruce needed to free her.

Batman attached his grapple to a space in the ceiling, pulling himself up to the roof and entering the air vents. He passed several patrols, but they did not notice him, as they were not searching the roof. Finally, he was outside the cell where Selina had been imprisoned. Bruce dropped to the floor, preparing to open the door with an automated lock pick. Reacting to the presence of someone behind him, Batman turned to see a man in a very silly looking outfit. The man was dressed in a suit adorned with stars and stripes, wearing a silly helmet, and carrying a round shield with a star in the centre.

Captain America flung his shield at Batman, but Batman ducked under it, flinging two batarangs at Captain America. Captain America sidestepped to avoid the batarangs, before catching his returning shield, charging with it. Batman jumped at Captain America, slamming both feet into the shield. The force of the kick sent both Captain America and Batman staggering backwards, but both regained their feet immediately. Captain America charged again, swinging his shield as a weapon, but Batman gripped the shield with both hands, before kicking Captain America onto the ground. Batman then flung two batarangs at Captain America, but they bounced harmlessly off Captain America's vibranium shield. Batman then slid along the floor, using his Taser on Captain America's shield, zapping him. Batman then gripped Captain America with his feet, throwing the Captain to the floor, flinging a batarang into his leg in the same movement. Before Captain America could fully recover, Batman threw a smoke bomb at him, and then kicked him hard in the face, stunning him.

Batman opened the door of the cell were Selina was imprisoned, before cutting the bars with a laser and freeing her. Batman and Catwoman then moved quickly and stealthily back to Batman's entry point, and the two of them jumped out, landing in a helicopter which Bruce had waiting nearby.

Reasons for this outcome:

1. While Captain America and Batman are very similar in terms of physical strength, speed and agility, Captain America is less intelligent, as Batman possesses a genius level intellect.

2. Captain America's arsenal is limited to his shield, whereas Batman's arsenal is far more varied, as he has many weapons that cover all areas, such as Tasers, smoke bombs, and anything money can buy.