Regarding a defender dropping to knees/hands with the intent of letting the oppoent trip over them, I think you have 4 legitimate options....all against the defender:
- personal foul (block)
- intentional personal foul
- T for unsportsmanlike conduct
- flagrant T
Which get's called really depends on the game. If it is clearly an act intended to harm the opponent...with our without contact...#4. If there is tension and I feel many players are on edge for whatever reason but absent intent to harm, #3. Put the hammer down and stop the silliness right there. If the game has been completely uneventful and it just seems like a goofy play out of nowhere, #1.