It is an offence if a player:
deliberately touches the ball with their hand/arm, for example moving the hand/arm towards the ball
touches the ball with their hand/arm when it has made their body unnaturally bigger. A player is considered to have made their body unnaturally bigger when the position of their hand/arm is not a consequence of, or justifiable by, the player’s body movement for that specific situation. By having their hand/arm in such a position, the player takes a risk of their hand/arm being hit by the ball and being penalised
GPT翻译比较准确，我就不手动了：
“
如果一个球员：
故意用手/手臂触球，例如将手/手臂移向球
在球使其身体变得异常大的情况下用手/手臂触球。当手/手臂的位置不是由球员在特定情况下的身体运动所导致的合理的情况下，球员被认为使其身体变得异常大。通过将手/手臂放在这样的位置，球员冒着手/手臂被球击中并受到处罚的风险。”
根本没有提到有没有意识、是不是折射。如果是摔倒的支撑手，也许可以认定符合“合理的情况”。
手臂定义：The rule reads, "the upper boundary of the arm is in line with the bottom of the armpit." There are also diagrams in the Laws of the Game to help with this concept.
胳肢窝以上算上臂，不算手球。胳肢窝以下都算。