Baby chicks often do this. One will fixate on something about the other one and injuries often occur. It needs to be stopped. Fortunately, it's not that difficult. Here's an article with some tips you may find useful.
https://www.backyardchickens.com/articles/aggressive-baby-chicks-and-how-to-stop-the-behavior.72029/
This past spring I had a problem with a chick pecking vents and causing significant injuries. I thought hard and came up with a couple of diversionary toys. One is a tennis ball with red dots drawn on it with red felt marker, and the other is a piece of weather stripping "noodle" stapled onto a block of wood with bright red duct tape bands. They worked to draw the chicks' attention away from chick vents.
The secret is to fashion a "toy" that resembles what the chicks appear to be fixated on. A fuzzy tennis ball may resemble somewhat a chick and the red dots will certainly hold their attention. The chicks really seemed to like playing with the noodle.
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