Yoga balls are not dangerous and can be taken to the subway.

Items that cannot be taken in the subway: guns and ammunition: pistols, rifles, submachine guns, machine guns, riot guns, air guns, shotguns, sports guns, props guns, starting guns, bombs, flares, etc. Control instruments: daggers, triangular knives (including triangular scrapers for processing), spring knives with self-locking devices, and other similar single-edged, double-edged knives and triangular sharp knives. And other knives that meet the standards for the identification of controlled knives issued by the Ministry of Public Security. Explosives: explosives, detonators, fuses, detonating cords, fireworks, firecrackers, smashing guns, drawing guns, smashing guns, distributing paper, etc.