Direct answer
At 9 weeks old, sudden bursts of running, grabbing, and biting can still fall within normal puppy behavior. If those frenzies reliably show up after a lot of activity or just before sleep, overtiredness or overstimulation may be part of the pattern.
When puppies get overtired or overstimulated, they often become more impulsive, mouthier, and harder to settle. Overtired puppies can lose some of their self-control the same way an overtired toddler does. At that point, continuing to correct or excite them may not help much; they may simply need less stimulation and a chance to rest.
Puppies also need a remarkable amount of sleep, often around 18–20 hours a day, and that rest supports normal brain and nervous system development. Regular naps can help prevent this kind of overtired behavior before it builds up.
In that moment, adding more correction may not be the most useful next step. A calm reset, such as some quiet time in the crate, and a chance to rest may help more.
Watch for the build-up, not just the explosion. If your puppy gets progressively mouthier, more frantic, and harder to settle after a long stretch of activity, that pattern is a useful clue that fatigue or overstimulation is contributing.
Also check the basics. Sometimes a biting puppy simply needs a potty break, so it’s worth ruling that out before assuming the whole episode is about training or fatigue.
Professional veterinary and training sources consistently recognize fatigue and overstimulation as common contributors to increased puppy mouthing. That doesn’t mean every biting frenzy is caused by tiredness, but it’s an important pattern to consider before adding more correction or more activity.