The jump putt is legal only if a supporting point is still on the lie at release. Stance rule, 10 m limit, balance, stance-violation risk and drills.
The honest answer: a jump putt is only legal if you release the disc while a part of your body still touches the ground at the lie. That follows from the PDGA stance rule: at the moment of release you must have at least one supporting point in contact with the lie, no supporting point closer to the target than the rear edge of the marker disc and all supporting points in-bounds [1]. An article from the Flying Disc Museum sums it up for the jump putt: it is legal if at least one toe stays on the lie until release [2].
The 10 m limit matters. Any throw from less than 10 metres from the basket is a putt [3], and there you must demonstrate balance behind the marker disc after the throw before advancing to the basket [3]. Beyond that line, according to the PDGA the rules allow jump and step putts in which you move past your marker after release, but a stance violation can be called if your supporting point leaves the ground before release [4].
Honestly: it is a risky throw. The museum article's author estimates many jump putts are stance violations, some experienced players say about a third; those are estimates, not measurements [2]. How hard is it? You need a secure putt and the courage to know the rules. There is no timeline.
The Graz handout calls putting not a classic throwing motion; it is unfamiliar at first, and 5–6 m is already a challenge [5]. Anyone who doesn't master their putt doesn't jump.
Milestone: From 8 m you make seven of ten standing putts (practice measure).
At least one supporting point in the lie, none closer to the target than the rear edge of the marker disc [1]. A supporting point is any body part that at the moment of release touches the ground or an object that gives support [6].
Milestone: You explain to a fellow player why both feet in the air is a stance violation.
Jump putts are, according to the PDGA, allowed outside the 10 metres as long as the stance rule is met [4]. Begin there, not with short putts. Within 10 m you first show balance behind the marker before going to the basket [3]. A jump over the marker disc there is a risk.
The disc is released while a supporting point still has contact. The museum article puts it: first release, then the foot may leave the ground [2]. Train with slow-motion video.
Milestone: On ten videos you see on each throw that the foot is still on the lie at release.
After the throw you land in control. Within 10 m you must show that you had balance under control behind the marker disc; you may fall while doing so [4]. Beyond 10 m you may go past the marker [4].
Tell your fellow players beforehand that you're attempting a jump putt. They judge whether the stance was valid, and a call must be confirmed by a second player [4]. The putt still counts, a stance violation costs a penalty throw [4].
Treat the jump putt as a rules exercise, not a show: the museum article even proposes extending the putting area to 20 m, because many putts now fall from there [2]. That is an author's proposal, not a current rule. Currently 10 m applies [3]. Whoever stays cleanly within the rule gets no penalty throws.
Yes, if you release the disc while at least one supporting point touches the lie [1]. Both feet in the air at release is a stance violation [2].
Within 10 m every throw is a putt, and afterwards you must show balance behind the marker disc [3]. Beyond 10 m, jump and step putts are allowed according to the PDGA as long as the stance rule is met [4].
Your fellow players: one player calls the violation, a second confirms it [4]. The putt still counts, but you get a penalty throw [4].
Yes, you only have to demonstrate balance, not maintain it; falling sideways or backwards is allowed [4].
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