Trent Alexander-Arnold

Trent was a footballer for Liverpool F.C., from an era the Thirteenth Doctor termed the "Klopp era", which included the year 2021. He played in a match between Liverpool and Barcelona, which was attended by the Doctor nine times by their thirteenth incarnation. On one occasion, they were a ball boy for Trent. (TV: The Halloween Apocalypse)

Behind the scenes

The Trent in question is of course Trent Alexander-Arnold, a right back for Liverpool. In the famous Barcelona game, which took place on 7 May 2019, Trent took a quick corner kick which resulted in a goal after several of the Barcelona defenders were caught unawares. The carelessness of the Barcelona players had been pointed out to Alexander-Arnold by a ball boy, which is implied in the episode to be the Doctor, but in reality is an academy player named Oakley Cannonier.