A tennis fan at the US Open has sparked a huge backlash after appearing to steal a player’s cap from a devastated young boy at the side of the court. 

Polish star Kamil Majchrzak was signing autographs for fans on court 11 after overcoming ninth seed Karen Khachanov in a five-set thriller when he took his cap off to give to a young fan. 

But a man standing next to the boy reached out, snatched the cap and quickly shoved it into his bag. The boy looked devastated and could be heard saying, “What are you doing?” 

Majchrzak was unaware of what had happened at the time, but after the clip went viral on social media he issued a plea to find the upset kid. 

“After the match I didn’t record that my cap didn’t get to the boy,” Majchrzak wrote on Instagram, along with screenshots of the incident. 

“Could you help me find the Kid from my match. If it’s you [or your parents see this], please send me a DM.” 

An hour later, Majchrzack said the boy had been identified and was “impressed by the power of the internet”. 

Fans on social media were quick to react to the clip with some speculating he is a rich businessman from Poland. 

One person said: “What a man-child. Disgusting and so disrespectful” while another said it was “shameful behaviour” and urged US Open officials to ban him. 

Majchrzak will face Leandro Riedi in the third round on Saturday morning.