In July 2011, Sinclair was named as the second head men's lacrosse coach in the program's history. In his first season at Randolph College, 2012, Sinclair tripled the program's win total from the previous three seasons combined. In his second campaign, he posted the team's highest win total in program history, capturing five wins, including two Old Dominion Athletic Conference (ODAC) wins, the first two ever.

The 2016 season was a banner year for the WildCats. The team set a program record of eight wins. The team just barely missed out on a berth in the ODAC tournament, but set other impressive feats. For the first time in program history, two members of the program were honored on the All-ODAC team, including the first First-Teamer in program history.

It was followed by a strong 2017 season, which saw the team earn several wins including a big-nonconference W over St. Marys's. Another athlete was honored on the All-ODAC team. In addition, for the third-straight year, a WildCat led the ODAC in caused turnovers, with this season it being done by Spencer Matthews.

In 2014, the WildCats earned two incredible overtime victories, the first two extra-session wins in program history, on the way to matching the program record for wins in a season.

Over the past four years, Coach Sinclair has established a tradition of competing on the field and in the classroom. Sinclair has coached 18 players who have earned undergraduate degrees from Randolph College, and 24 ODAC All-Academic Team Members. On the field, Sinclair has directed one All-ODAC Second-Team Player, three All-ODAC Third-Team Players, one First-Team ODAC Player of the Week recipient, and two All-ODAC Sportsmanship Team Players.

Sinclair came to the Randolph program after serving as the head boy’s lacrosse coach at Winter Park High School in Maitland, Fla. While at WPHS, Sinclair guided his program to a 61-14 record over his four year tenure including three district championships and appearances in the state playoff series three times. Sinclair also has produced numerous collegiate players while at Winter Park.

Before taking the post at Winter Park, Sinclair worked as the top assistant at Christopher Newport University, where he helped develop a new program. Sinclair recruited players that accumulated 34 wins in the first five years of the program at CNU, and was also directly in charge of monitoring academic performance.