Flag Shirt Market Report: Sales Volume, Market Share, Leading Brands & Market Trends

Under Armour is the best-performing flag shirt brand in July 2026, moving 1,900 units across 5 ASINs for 36.5% of Top 10 volume. ROSTIVO follows with 1,000 units (19.2%), ahead of Ann Arbor T-shirt Co. on 1,000 units (19.2%).

With 6 brands splitting the Top 10 and 75.0% of volume sitting with three of them, this is a concentrated shelf — the leaders hold multiple listings or one very high-velocity ASIN, so a new entrant competes against established review moats rather than an open field. Average selling prices among the leaders run from $5.99 to $21.29, which frames the price band a competing listing has to justify.

Based on July 2026 data, this shortlist surfaces the two kinds of ASIN worth keeping an eye on — the ones that just broke into the Top 10, and the ones growing fastest month over month. Specifically, 3 ASINs forced its way in: B0DH723V35 booked 800 units at $16.98, with ▲ 60.0% MoM change.

The two signals carry different weight. A fresh entrant means share has already changed hands — an incumbent gave up its place to make room, so any competitive set drawn up a month ago is now out of date. A steep growth rate works as the earlier warning: it marks demand that is still compounding, usually a month or two before the ranking catches up to it.