Grima has extensive experience in the NRL as an assistant coach at Parramatta Eels, Cronulla Sharks and the St George-Illawarra Dragons.
After taking over from Rea, Grima won his first game against Super League giants Leeds Rhinos 40–36 at The Hive.
On 9 October 2014, London Broncos announced Grima had signed a 2-year contract extension to keep him as head coach until the end of 2016.
Grima returned to Australia and was signed as Brad Arthur's assistant coach with the Parramatta Eels for the 2016-17, 2017-18 seasons.
In May, 2023 to aid with the unveiling of the NRL's 18th franchise in 2027, Grima assumed the task of managing elite development and pathways in PNG.