Theobald made his debut in county cricket for Norfolk against the Kent Second XI in the 1930 Minor Counties Championship. Prior to the start of World War II in 1939, he made a total of 50 appearances for the county in the Minor Counties Championship.[2] In 1938, he made a single first-class appearance for a combined Minor Counties team against Oxford University at the University Parks.[3] He batted twice during the match, being dismissed for 41 in the Minor Counties first-innings by Mervyn Austin, while in their second-innings he was dismissed for a duck by Edward Scott.[4] Following the war, he resumed playing Minor counties cricket for Norfolk, making a further five appearances for the county, the last of which came against the Surrey Second XI in 1947.[2] During his time playing for Norfolk, he also shared in a Minor counties record first-wicket partnership with David Walker of 323.