There's a hierarchy with ball boys/girls at Wimbledon this year. The ones that handle the tennis balls have smart blue and white Ralph Lauren Polo uniforms. The ones that hold umbrellas, supply drinks and "ice scarves" have smart green and white, Ralph Lauren Polo uniforms. If you watch the tennis, you may see several of these, "suspicious looking characters," dressed in Wimbledon uniforms, sitting behind the players chairs. They aren't security, those are dressed differently. I can only guess they are "emergency line judges," in case the Hawkeye system goes tits up. Wimbledon think of everything.
