My cousin does that. In gulli cricket. He counts the score out aloud in tight matches too, and applauds every delivery from the bowler when in the fielding side. Some batsmen (those who can actually bat) usually respond by counting the score themselves after they hit a boundary. Usually makes for some funny scenesI'm more of a fan of the psychological sledging. Telling them they're under pressure, making them believe they're useless and giving the bowler encouragement instead of just saying stuff like "i rooted your mum last night"