Larry is exhibiting the defense mechanism known as Identification
Identification is a defense mechanism where an individual unconsciously takes on the characteristics, feelings, or behaviors of another person or group that they admire or identify with. In this case, Larry, who did not participate in sports himself, identifies closely with his school's sports teams.
By wearing the school's colors, cheering for the team, and feeling exhilarated when they win, Larry is psychologically aligning himself with the team and deriving a sense of belonging and accomplishment from their success, as if it were his own. This behavior allows Larry to cope with any feelings of inadequacy or unfulfilled desires he may have regarding his own athletic abilities.