Jaehyun's Cute Pitching Challenge with Jaemin

Why Koreans care

A ceremonial first pitch is a guest appearance, not a place on a team's playing roster. The thank-you for JAEMIN's pitch and request that he return as an owner extend the baseball occasion into playful fan appreciation, rather than announcing a new career.

In the Korean comments

Fandom, baseball wordplay: “Beauty and the beast—I mean, an outfielder.” Fandom, appreciation for the visit: “JAEMIN, seriously, thank you for coming to throw the first pitch.”

What the words mean

야수 (yasu, beast or baseball fielder) supplies the pun in the first quote. The writer explicitly specifies outfielder, so the beast wording is not simply an insult aimed at the athlete's looks.