How to disable tap to drag?

If this is a newer MacBook Air (with a Force Touch trackpad), changing the pressure required to "Click" should help fix this. I experienced similar issues on my MacBook Pro.

Go into System Preferences, click the Trackpad icon, and select the "Point & Click" tab. On the left you should see a "Click" slider with "Light", "Medium", and "Firm" options. If you shift it over one setting, you might find that's enough to fix the issue.

Alternatively, disabling Force Click and haptic feedback (unchecking the checkbox at the bottom), may also stop peculiar behavior from happening. That's ultimately what I ended up doing and it made a world of difference in my case.