A footballer selling hair ties sounds like a novelty. It is a textbook brand extension, and the legal work behind it decides whether it makes money or merely attracts copies.
What is being sold
Not an accessory. An association. The product works because a recognisable person uses it visibly, and consumers buy the connection. That connection is built from a personal name, an image, and often a distinctive product appearance.
The three rights involved
Trademark over the product name and the athlete name, filed in class 26 for hair accessories and any adjacent class. Image rights, licensed in writing from the individual to the company selling the product. Industrial design where the product itself has a distinctive appearance worth protecting.
Where these ventures go wrong
The product launches on the strength of attention, sells out, and within weeks marketplaces are full of copies. Without a registration there is no takedown mechanism, because platforms act on registration numbers rather than on explanations.
If you are planning a brand extension
File in the new class before you launch, not after. Your existing registration for one category does not cover a different one, and the window between announcement and copy is now measured in days.