A Shirley Boys High School alumni, Grigg came to teach at Nelson College in 1996. Taking over as coach of the 1st XV in 2000, the team achieved a Quadrangular Tournament win the following year under captain and future Mako centurion Robbie Malneek. In the 20 years Grigg has been involved as coach or manager of the 1st XV, Nelson College has enjoyed a number of successes on the field – winning the Moascar Cup, Crusader secondary schools titles and making the Top 4 national 1st XV finals – to go with six Quad wins and four in the last six years. He has also been instrumental in the school’s rugby academy programme, which combined academic school study with specialist rugby coaching that had set many boys up for higher honours in the professional ranks.