With the release of Blue Lock chapter 251, the manga revealed Rin Itoshi and Nanase Nijiro's flashback as to how Rin trained Nanase to become his pawn. Following that, it seemed like Rin was about to score, however, Bastard Munchen players managed to stop him. But the person to block his shot was neither Isagi nor Kaiser.
The previous chapter saw Isagi and Charles identify each other as Meta Vision users. Hence, Charles challenged Isagi to see which of the two midfielders was able to control the match. In the meantime, Kaiser was about to place his Kaiser Impact Point shot. Unfortunately for him, Rin stopped the shot by sweeping away the ball from Kaiser's feet.
Disclaimer: This article contains spoilers from the Blue Lock manga.
Blue Lock chapter 251 reveals Nanase's ambidexterity

Blue Lock chapter 251 saw the manga resume right from where the previous chapter ended. Rin Itoshi stole the ball away from Michael Kaiser and began his attack. Right when he began his attack, his path was blocked by Kunigami Rensuke and Alexis Ness.
Nevertheless, Rin managed to dribble past the two players and Raichi Jingo. This left Ness and Raichi shocked by Rin's display of skills that had him showcase his touch, speed, technique, and reading. Right after, Charles and Tokimitsu arrived to back up Rin. However, Rin ignored both of them and seemed much more interested in teaming up with Nanase Ninjiro.

Blue Lock chapter 251 then showed fans a flashback of Rin and Nanase. After not getting picked for the starting lineup, Nanase Nijiro was desperate to improve. Hence, he asked Rin to make him his disciple. However, Rin believed that Nanase was a really bad player, with no real redeeming qualities. Thus, he rejected the request.
However, Nanase was adamant on improving kep requesting Rin. He even conveyed to Rin that he could mold him into any form of player he needed. This managed to grab Rin's interest. Following that, Rin helped Nanase with his training. Soon after, Rin realized that Nanase's left foot worked nearly as well as his right foot. Thus, he theorized that Nanase might have been inherently ambidextrous.

Blue Lock chapter 251 then switched back to the match as Rin passed the ball to Nanase. Nanase dribbled the ball forward. However, his path was blocked by Mensah and Kiyora Jin. While in normal situations, a player might have been forced to pass the ball back, Nanase's ambidexterity allowed him to play a pivot role from any part of the field. Hence, he crossed the ball to Rin.
Just as Rin received the ball, he complimented Nanase's growth and prepared to shoot the ball. However, his path was blocked by a team-up of Kaiser and Isagi.

Apparently, Rin was waiting for this as he had promised Isagi a special seat to watch him become the best striker in the world. Thus, Rin picked up Isagi by his collar, lobbed the ball into the air, and volleyed it toward the goal.
Unfortunately for Rin, the shot was blocked by Hiori Yo as he was easily able to read Rin's movements. With that, the manga set up Hiori Yo as another strong player in the match.