Canadian Tai Chi Academy
Traditionally, push hands practice is the beginning of the interactive martial arts training in tai chi and is usually introduced after the student learns the bare hand form. It begins with fixed step, single hand practice and progresses through two hands, fixed step and two hands "walking" practice.
While there is certainly a potential for competitive practice, our focus is in using the various push hands practices as a tool to measure and improve your tai chi practice. Your partner can help you strengthen your muscles and loosen your joints more quickly than you can generally achieve alone doing the single person forms.
The basic elements of push hands are easily recognized in the tai chi move "Grasp Bird's Tail", but at a more advanced level almost any movement from the form may be involved and the student being pushed or pulled may need to be able to do front or back rolls on the floor to avoid injury.
Master Moy encouraged us to push hands regularly and with partners of varying abilities. Some of the techniques he taught are expressly forbidden in formal push hands competitions and he discouraged us from participating in those events.