Napgate means: A 2010 controversy in which Ken Griffey, Jr., of Major League Baseball's Seattle Mariners, was reported to have been asleep in the clubhouse during a game.. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. It is sporting vocabulary and harmless in itself. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.