Can a fielder that has the ball tackle a runner in order to prevent him from getting back to a base and tag him out? For example a runner is caught in a run down between 3rd and home, the runner is sliding back to the base when the catcher dives and with his free arm grabs the runner around the neck preventing him from reaching the base and then tags the runner. Is this obstruction ? Is it legal?

Wow.. sounds to me like the catcher would be thrown from the game.. I would say the only way something like this could legally happen.. is if the catcher was diving for the tag.. but because he wrapped his arm around the kids neck.. i would award the run.. and toss the catcher

Sounds more like a TAKE DOWN. Do believe
I would have to award the runner home, and
tell the catchers coach you new a new catcher
cause that one is in the pentaly box. :)