The boy is believed to have been taking part in a one to one football training session on the field at the end of School Road, South Shore, when he was hit at around 5.05pm today, May 11.
Police ambulance and air ambulance services were called to the scene, and he was taken to hospital with serious injuries.
Police have now confirmed he has died.
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A police spokesman said: "A nine-year-old boy has sadly died following an incident on a football field shortly after 5.05pm today. Although enquiries are still ongoing, we believe the boy was struck by lightning. Our thoughts are with the boy's family at this sad time."
Det supt Nick Connaughton said: "This is a truly devastating incident and our thoughts are wholeheartedly with the family and friends of the young boy, who has passed away, at this very sad and distressing time."
In a statement posted online, the Spirit of Youth Junior Football Club said: “It is with deepest regret that we have to report the news that the young boy who was struck by lightning earlier this evening has sadly passed away.
“The tragic incident happened on our home ground at Common Edge playing fields but it was not during a club training session. As a club, we are heartbroken and we offer our deepest condolences to the boy’s family.
“Spirit of Youth is a family and we are entrenched in the local community, and we will give whatever support is required to both the family and to those that were with him at the time.”
Anybody with information about the incident, or who witnessed it and has not yet spoken to police, is asked to call 101 quoting log 1169 of May 11.