A ball striking device, such as a golf club, includes a head with a face having an outer surface configured for striking a ball, a body connected to the face, and a channel located in the body. The channel is configured to influence the characteristics of the impact of a ball on the face, such as by flexing or compressing in response to the force of the impact, exerting a response or reaction force on the face, changing the motion or behavior of the face, and other manners. The head may also include a pair of channels that have a gap between them.