100 km/hr

 SCP-018 was noted to be able to bounce with extreme height. At first thought to be a pleasant child's toy, SCP-018 was able to bounce with over two hundred percent (200%) efficiency (that is, if dropped one (1) meter, it would bounce two (2), then four (4), then eight (8), then sixteen (16)). The ball soon became a dangerous projectile, reaching speeds estimated at over 100 km/h and damaging property and injuring five (5) in the city of █████████████.