简单说一下新版STEP-BACK走步规则。
左脚往后踩收球，右脚收回来是新版的轴心脚。（新版明确规定收球后两脚落地时，后着地那只，旧版看收球，所以看时机，不易判断）
这时左脚再往后踩到三分线外，右脚不动或是离开地面落地前出手都不算走步，是好球。
Harden和Curry都是第二步另一只脚收回来着地才出手，所以都是走步。
※ 引述《josherion (Josh)》之铭言：
: https://www.thescore.com/s/8673443
: Steph Curry held up James Harden's No. 13 to his chest after getting called
: for a traveling violation on a clearly illegal double step-back Saturday
: night against the Sacramento Kings.
: The Golden State Warriors sharpshooter must have been taking notes when
: Harden got away with the move when facing the Utah Jazz on Dec. 17, although
: he was unable to get one over on the referees when he performed it.
: The 30-year-old finished with 42 points in a 127-123 Golden State victory,
: marking his fourth 40-point outing of the campaign and 34th of his career. He
: also connected on 10 3-pointers on 20 attempts, which is the 11th time he's
: ever drilled double-digit shots from behind the arc.
: 在今天比赛第四节中, Curry在一次进攻后撤步投三分时被吹了走步.
: 他随后在胸前比了13, 以示抗议.
: https://twitter.com/SLAMonline/status/1081783784398376960
: 让我们来回顾专业的step-back 3分球...
: https://twitter.com/ESPNNBA/status/1074871763115356160