After participating in the traditional annual Fastern's E'en Ba game, he became interested in the similar game of rugby union, joining the local Melrose RFC side in 1880, initially playing for the seconds before making the first team and also playing for South of Scotland.
In 1883, with the club short of funds, Haig suggested hosting a tournament as part of a sports day to raise money.
The immediate success of the tournament meant that other clubs in the Borders region also set up their own rugby sevens competitions.
After Haig retired from competition, he continued to take an active part in the running of the club, serving for several seasons on the General and Match committee.
In 2008, Haig and Melrose RFC were honoured for their role in the creation of rugby sevens with induction to the IRB Hall of Fame.