#!/bin/bash
s='id,name,sport
100,Pau Gasol,basketball
101,Tiger Woods,golf
102,Yao Ming,basketball
103,Nadal,tennis
104,LeBron,basketball'
sed -r 's/(.*),([[:alpha:]]*[[:space:]]*[[:alpha:]]*),(basketball)/\1,\U\2\E,\3/' <<< "$s"