Why does the Torah add the words "Asher Yamus bah" here and in Pasuk 18?
Rashi #1 (citing Targum Onkelos): With reference to a stone 1 that fills the hand and a wooden object that is sizeable, the Torah is teaching us here that, if Reuven murders Shimon with an object other than metal, he is only Chayav Misah if Beis-Din assess that the object with which he killed is sufficiently large to have caused his death (and if it strikes him on a limb that the stone is liable kill
Rashi: To preclude from the notion that "O be'Even asher Yamus bah" (Sh'mos 21:18) and "ve'Chi Yakeh Ish es Avdo ba'Sheivet" (Ibid. 21:20) are referring to a stone or a stick, irrespective of size.
What do we learn from "Even Yad"?
Rashi: It is a stone that fills the hand. 1
Ramban (Hilchos Rotze'ach 3:2): We evaluate [the murder weapon, and also] the hand 2 that threw it. Something thrown from afar impacts less than something thrown from close.
Ba'al ha'Turim: Even Yad must be evaluated. Even ha'Melech (the wing's weight) 3 need not be evaluated. Surely it can kill!
QUESTIONS ON RASHI
Rashi writes that "Even Yad" is a stone that fills the hand. We already know from "Asher Yamus Bah" that it must be able to kill!
Gur Aryeh: If the murder weapon sometimes kills and sometimes does not, we cannot kill the murderer. A stone that fills the hand, it always kills. 1
Perhaps a stone that fills the hand must be evaluated, but anything bigger can surely kill, and need not be evaluated (refer to 35:17:151:3). Or, a stone that fills and is thrown by hand must be evaluated, but a rock thrown via a slingshot need not be evaluated (surely it can kill)! (PF)
It is astounding to say that such a rock always kills. Surely it need not kill if it is thrown softly, or if it landed not on his torso or if it just nicked his skin! One who must be stoned, if he did not die from the fall, they dropped a giant rock, that needs two people to carry it, on him. If that does not kill him, everyone stones him