DISCLAIMER: I do not own Dragon Ball Z or DC Comics.

Frieza lay on his back in the air, casually daydreaming. Frieza was above the water, hovering over the middle of the ocean. Frieza casually tossed a Ki blast into the water which sent a giant burst of water into the air. He then fired a series of smaller ones to blow up the fish that flew out of the water. He caught three fish in his hands and feet, and quickly ate the live fish.

Aquaman sensed the disturbance, and quickly swam up to the surface where he found a small white alien hovering above the water and still chewing a fish tail. Aquaman jumped out of the water at Frieza and punched him, launching him into the sky. Frieza righted himself and turned to glare at the one who had hit him. Aquaman called two sharks to float under him so he could stand on them. Frieza hovered down closer to the water, and smirked.
"Do you know who I am?"
Aquaman floated closer to Frieza, readying his trident.
"I am the King of Atlantis, so it doesn't matter who you are."

Frieza smirked and flew higher, firing a blast into Aquaman and launching him down into the water. Aquaman returned to the surface and launched himself up, flinging his trident at Frieza at the highest speed he could muster. Frieza attempted to dodge the trident but was hit in the stomach. Aquaman jumped out of the water at Frieza, but Frieza fired another blast into Aquaman, pulling the trident out of himself and throwing it into the water, snarling as Aquaman swam under the water and then returned to the surface with his trident.

Aquaman called a much larger shark under him, allowing him to stand taller in the water.
"You are wounded. Surrender and I promise not to kill you."
Frieza smirked. "Kill me? You… kill me?"
Aquaman jumped out at Frieza and caught him by the tail, but Frieza flew higher and was relieved to see Aquaman lose his grip on Frieza's tail. Frieza then flew closer and started punching Aquaman at high speeds, hitting the much slower yet much stronger opponent repeatedly. Aquaman attempted to catch Frieza several times, but Frieza knew better than to let himself be caught. Frieza then caught Aquaman and placed him in a shield composed of Ki.
"How about a little game? The game finishes when I miss and put you in orbit!"

Frieza kicked the shield up into the sky, flying past it and kicking it back to the ground, and flew past it again, kicking it up into the sky. Frieza repeated this process several times, before Aquaman stuck his trident into the shield, shattering it. Aquaman swung his trident at Frieza in midair, who flew back and glared at Aquaman, firing a small Ki blast which Aquaman took in the face. Aquaman dropped back to the water, calling up a horde of sharks from under the water and sending them up towards the now low-hovering Frieza, who flew through the crowd of sharks killing them with strikes and blasts.

Aquaman jumped out of the crowd of sharks and caught Frieza by the shoulders, punching him in the face and sending a sliver of blood from the Icegen's mouth. Frieza fired a blast into Aquaman's face, but Aquaman's grip tightened, prompting a scream from Frieza. Frieza started punching and kicking Aquaman at piston speeds though to no avail, but then another thought occurred to him, and he started flying at top speeds towards the atmosphere, reaching low orbit in a few seconds. Aquaman tightened his grip at first, but then let go as he realised outer space would be a death sentence for him.

Aquaman dropped down towards the water while Frieza rubbed his horribly bruised shoulders. Snarling with rage, Frieza powered up greatly, reaching about 80% of his full power. As Aquaman hit the water, Frieza continued to power up, entering a process which took several minutes as he powered up to his maximum, bulking up significantly. Down in the water Aquaman attempted to jump high enough to reach Frieza, but Frieza was in low orbit still, where he knew Aquaman couldn't reach him. Seeing this, Aquaman dropped back under the water and called a horde of sea creatures while also making sure he was adequately hydrated.

Frieza finally reached full power, and flew down to attack Aquaman, who stood on a giant shellfish surrounded by many others. Aquaman flung his trident at Frieza, but Frieza dodged the attack and fired a string of blasts at the shellfish, blowing them up one by one. Aquaman held out his hand and his trident flew back to him, and he jumped up at Frieza, ready to impale him. Frieza flew higher and held up his hand, charging a Destructo Disk.
"Lights out, fish man!"

Frieza flung the Disk at Aquaman, who blocked the projectile with his trident, but found another Destructo Disk flying at him as soon as he blocked the first one. Aquaman dived under the water and swam away from the Disk, but it caught up to him and slashed clean through his back. Aquaman drifted back to the surface, his trident dropping from his grip and his torso sporting a deep cut through half of it. It was only because of his huge shoulders that he had survived at all, and his wound was almost fatal. Frieza was unable to sense Ki and thus assumed Aquaman was dead, and started to fly away when a flash of movement signalled the arrival of Superman and Goku.

Frieza turned and flew away as fast as he could, but found Goku in front of him punching him back to the waiting Superman, who trapped Frieza in a headlock. Goku hovered closer to Frieza and punched him once, shaking him to his core. Superman punched Frieza in the back, causing an audible crack and causing Frieza to scream. The Saiyan and the Kryptonian watched as Frieza passed out, and Superman quickly flew him to the Watchtower while Goku used his Ki to heal Aquaman.

Analysis:

Aquaman possesses a huge advantage in strength, and can take Frieza's blasts as he can take hits from Superman, but that is where his advantages end. While it is true Aquaman's strength being almost equal to Superman's means his thrown trident can be expected to be at least fast enough that Frieza will have trouble dodging it, his actual movement speed is sadly lacking compared to Frieza's.

While Frieza's strikes and blasts will not bring Aquaman down easily, Frieza has the Destructo Disk, which, while Aquaman probably could block it with his trident, once it hits him it will cut him apart. Frieza can also easily charge these attacks since he can fly and go into orbit, which Aquaman can't do, and thus Frieza can easily get to safe distance and start attacking at range, though his inability to sense Ki means he will need to come close enough to see Aquaman, at which point Aquaman can attack back.

Finally, the best way for Aquaman to win was by catching Frieza and crushing him, and in theory once he's caught him Frieza can't get free, but Frieza can fly up into space, forcing Aquaman to either let go or asphyxiate and dehydrate. Once Frieza starts shooting Destructo Disks Aquaman's seconds are numbered, since while he can react to them to some extent due to the charge up time required and his trident should be strong enough to block them, he will be hit long before Frieza runs out of energy, and Frieza can charge up another while Aquaman struggles to block the first one.

Note that the field was the ocean so that Aquaman had his natural domain and full power to control, since Frieza can fly anywhere so it made sense to let Aquaman use his swimming and water abilities.