I would call this illegal if I did a bike check although no rules seem to address “unnatural shape that could injure or otherwise cause damage”
This is discguard from PRAAAP Bike Polo equipment. (Edited, sorry Chris and Stubborn, my mistake)
Please tell me if I’m wrong
1.3.4. Bicycles
1.3.4.1. 1.3.4.2. All bicycles must have at least one hand-operated braking mechanism.
Handlebars must be a maximum length of 710mm at the longest point, including grips and plugs.
1.3.4.2.1. Handlebars must be plugged or capped.
1.3.4.3. All sharp edges must be removed or covered.
1.3.4.3.1. Disc brake rotors must be protected.
1.3.4.3.2. All cogs and chain rings must be covered by the chain or protected from being openly exposed.
1.3.4.3.3. 1.3.4.3.4. 1.3.4.3.5. Cable ties must be left uncut or cut in a way that there are no sharp edges.
Exposed threads on bolts and axles must be filed down or covered.
Cable guides, v-brake posts and any other sharp accessories welded onto the frame must be either removed or covered.
1.3.4.3.6. All covered parts of the bike must be approved by the Head Referee.
1.3.4.4. There can be no racks, fenders, bottle cages or any other accessories that may aid in blocking the passage of the ball.
1.3.4.4.1. Wheel covers, disc guards, and round chain guards are permitted.