This action is an example of affect display or kinesics.
Explanation:
Affect display is an example of non verbal communication in which <u>someone does some gesture from their body or face that betrays their emotional state or what they are thinking.</u>
It is evident in the passage that the batter is
nervous
eager to outplay the pitcher
The biting of the nail while watching the pitcher closely is a telltale sign of this.
