(I'm not super well versed with either the Naruto or DBZ universes, but I will try from my little knowledge)

Krillin approached the stage, his eyes glued to the floor.

"So," Itachi said, "you know my ability. It appears my reputation precedes me by quite a lot these days."

Krillin nodded as he got into his fighting stance.

"Straight into this then." Itachi said as he started doing his hand signs.

The announcer yelled across the stadium "Ready? BEGIN!"

Itachi immediately used shadow clone jutsu to confuse Krillin and give himself a feel for how powerful his opponent is. Krillin took the bait, assuming it was some kind of trick, decided to attack the closest one with a punch to the gut. After it landed, he relentlessly hit the clone until it was out of the ring.

As Krillin focused on his target, he failed to notice the other ones closing in. He turned around to meet a wave of fireballs headed straight towards him. He jumped up, very confused but quickly realizing they were all real.

Itachi was surprised by his speed, but took the opportunity to throw shurikens at him while he was in the air. Krillin dodged these with relative ease.

Itachi started to get another attack ready when his clones started falling. Krillin said behind the last Itachi "Good fight, you sure got some cool abilities." Before punching him in the back and knocking him out.