Legal Swing (ASA OR U-Trip)

[Larks]

Hey Softball guys,

Larks here...basketball guy but softball player....quick question....

How do you guys usually judge a swing to be legal?

What I am referring to is the slow or bunt swing in softball.

Is it follow thru meaning the swing may be slow and as long as it doesnt stop, it's legal?

Also, do both hands have to remain on the bat? Example, can the batter remove his top hand in order to complete the slow swing? (Letting go with top hand roughly half way thru the swing.)

Is this rule any different in USSSA vs. ASA?