Dallison began his career playing the youth teams at West Ham United and Arsenal before signing a contract with Brighton & Hove Albion in October 2013 following a successful trial.[5][6] He spent time out on loan at non-league sides Dartford and Braintree Town in 2015.[7][8] In February 2016 he joined League Two side Crawley Town on loan.[9] He made his professional debut on 20 February 2016 in a 1–1 draw against Plymouth Argyle,[10] but broke his foot after 60 minutes, ruling him out for the rest of the season.[11]