A 15-year-old girl was hurt in a "malicious attack" when a pint cup filled with coins was thrown during a football match, police have said.
Greater Manchester Police said the incident happened at about 20:25 GMT in the Etihad Stadium at the EFL Cup tie between Manchester City and Liverpool on 22 December.
The force said the cup was thrown from an upper tier to a lower tier.
The girl was treated in hospital for a head injury, officers said.
Sup Int Gareth Parking said the force would "not tolerate violent or malicious behaviour in any situation, this does not exclude football matches or sports games".