Sanhedrin (74a) If one pursuer was pursuing another pursuer in order to save him, i.e., if he was trying to save the person being pursued by killing the pursuer, and while doing so he broke vessels belonging either to the pursuer or to the one being pursued, or to anyone else, he is exempt from paying for them. The Gemara comments: This is not by strict law, as if one who saves himself at another’s expense is liable to pay for the damage, certainly one who saves another at the expense of a third party should bear similar liability.
This is also mentioned in bava Kamma without mention of Takkana
Bava Kamma (117b) And with regard to a pursuer who was chasing after another pursuer in order to save the latter’s intended victim, and he broke vessels during the chase, whether they belonged to the pursued individual, i.e., the individual attempting murder, or to anyone else, he is exempt from payment. The Gemara notes: And this is not the halakha by Torah law, but if you do not say so, you will not have any person that saves another from a pursuer.
Shulchan Aruch (M 380) doesnt say there is a takkanah
ואחד שרדף אחר הרודף להציל את הנרדף ושבר כלים בין של רודף בין של כל אדם פטור כדי שלא יבואו מלימנע מלהציל את הנרדף:
While the gemora and Shulchan Aruch simply note that we ignore the halacha in this case the Rambam asserts there is a Rabbinic decree to ignore the Torah rule in this case. None of the comentaries mention this assertion of the Rambam
Rambam (Chovel Umazick 8:14) (When a person pursues a rodef to save the person he is pursuing, and in so doing breaks utensils - whether those belonging to the rodef or those belonging to another person - he is not liable. This does not follow the letter of the law, but is a Rabbinic ordinance, enacted so that a person will not refrain from trying to save his colleague, or will hesitate and proceed carefully while he chases after the rodef.
רודף אחר רודף להצילו ושיבר את הכלים בין של רודף בין של נרדף בין של כל אדם פטור ולא מן הדין שאם אי אתה אומר כן נמצא אין לך כל אדם שמציל את חבירו מיד הרודף: