[2] Sinclair attended Scotch College with future St Kilda teammate Jack Billings.

[6] Of the mentoring, Sinclair stated that "being able to work with him on a wing, I’ve learned a lot from him....It’s been great having him around, just with little things like sitting in on my reviews and trying to help me out.

Ahead of the 2018 season, Champion Data ranked Sinclair as one of the AFL's 55 'elite' footballers, with his inside game, his pressure and his scoreboard impact listed as he key traits.

After spending his career to date as an offensive player in the midfield or at half-forward, Sinclair was switched to the backline ahead of the 2021 season.

Sinclair notched up his 100th AFL game in Round Two, where he was ceremoniously handed his guernsey pre-game by Tony Lockett.

At the midway point of the season, Sinclair was First for St Kilda's intercepts (99), second for goal assists (eight), third for rebound-50s (46), contested possessions (99), defensive-half pressure acts (123), ground-ball gets (75).

[11] Sinclair backed up his excellent 2022 season in 2023 with a second All-Australian selection, the customary Scoops Medal and a second best and fairest.