The tip should make a brief contact with the cue ball. If the cue follows through while still touching it, or contacts it again, the stroke may be a push or double hit under the discipline's rules.
Double-hit risk
The danger is greatest when the cue ball is very close to the object ball. Once the first contact occurs, the cue ball is moving and the tip can catch it again. Avoid driving through; use a thin separating stroke or ask the referee to assess the layout.
Signs of a push
Long cue-ball contact, a tip that appears to stay on the ball, or a hand moving forward with it can look like a push shot. A free pendulum stroke and a short contact reduce the risk.
Do not stop balls by hand in competition. Freeze the situation, call the referee and apply the rule set for the actual discipline.