When the disc needs to be walked to a location before setting a pivot (for example, when the disc lands out of bounds, walking to the brick mark, or walking the disc to the goal line after a turnover in an end zone), there should be a ground tap.
I think this would help remove any ambiguity about when the disc is in play by using a very simple visual signal that many players already use anyways because of USAU rules.
There are a number of situations where this would be helpful (this is not an exhaustive list):
1. When some players are uncertain as to where exactly where the disc is coming into play. It can sometimes be difficult to tell where exactly a disc went out of bounds, or the exact location of the brick mark, especially on a field without lines or painted brick marks.
2. It would prevent throwers from "taking the defense by surprise." Just as an example, under the current rules, it is possible for the thrower to walk (or run) to where the pivot should be established and immediately throw while still in motion (as long as their pivot is on the ground through the throwing motion).
3. It would prevent throwers from potentially taking a running start into a throw (for example, after picking up a disc in their own end zone).
4. It creates a much clearer instant for when the stall count should start. Often, especially at intermediate levels or lower, I see players unsure about when they should start counting stalls or looking to attempt a throw. A simple ground tap would easily clear up this confusion.
This would be a very simple change that would not impact the game, but would greatly improve on-field visual communication. The thrower will still be able to start play without delay after establishing a pivot at the correct location. This would just be a really simple way to signal to everyone, including sideline players, game advisors, and fans, that the pivot has been established, the stall count has started, and the thrower is now looking for a receiver. Currently, I believe there is unnecessary ambiguity for when exactly this action (establishing the pivot) has taken place. This signal is already used in countries around the world (not just in the US) because it helps with communication, so it would be extremely easy to implement.
I am ambivalent about this. I firmly believe that it's on defenders' shoulders if they aren't ready for a disc to be brought in in non-check situations. However, you are right that ambiguities about where the disc is coming in are problematic. That said, ground taps are not free and I would prefer to allow throwers to keep that first second of their stall - being able to take advantage of lazy defenders is a feature, not a bug.
I agree that in competitive games, throwers taking advantage of lazy defenders is fine. I just feel that for most levels, and also for non-players, this is a really simple way to improve communication and reduce ambiguities.
I disagree that a ground tap takes a full second to do - at its absolute slowest, it might take the same amount of time as saying "stalling." I've already seen tons of players across all levels do the ground tap anyways, with no impact on the game itself, just because it helps to let everyone know that a pivot has been established.