The Ramban says that there is a light proof that the beginning with neglect and the end by force which is obligated in damage does not apply to a case in which the beginning is with minimal guarding, and then later cames force. The proof he brings on page 93 of Bava Metzia is the teaching on page 45 in Bava Kama, "Four come in place of the owner: a borrower, renter, paid guard and an unpaid guard. If an ox has been warned three times, and goes and kills someone, the ox is killed and 3 kinds of guard pay the fixed penalty and pay back to value of the ox to the owner except for the unpaid guard who does not pay back. The Gemara decided the braita is taking about a case where all four guarded the animal with minimal guarding. Also, the gemara says that according to R. Elazar, that an animal that has already proven dangerous must be slaughtered, and our mishna is referring to such a case. On one hand, I can see the point of the Ramban because the paid guard did a minimal amount of guarding, but all should have done the proper amount of guarding. so only the unpaid guard is not obligated to pay. However, it seems hard to understand. The reason I say this is the entire law of the "beginning by by neglect and the end with force is obligated to pay" is referring to the paid guard. It cannot be the unpaid one because in any case he is not obligated where he did minimal guarding. so, it must refer to the paid guard. But he is obligated in the braita even though he did minimal guarding. so how can you decide from a case where he is obligated to pay even though he did minimal guarding to a case where he also did minimal guarding and yet say he is not obligated.______________________________________________ The רמב''ן says that there is a slight proof that תחילתו בפשיעה וסופו באונס חייב does not apply to a case in which the beginning is with שמירה פחותה, and then later came force. The proof he brings on page צ''ג of בבא מציעא is the ברייתא on page מ''ה in בבא קמא four come in place of the owner: a borrower, renter, paid guard and an unpaid guard. If an ox has been warned three times, and goes and kills someone, the ox is killed, and the four kinds of guard pay the כופר and pay back to value of the ox to the owner. That is all three except for the unpaid guard who does not pay back. Theגמרא decided הברייתא is taking about a case where all four guarded the animal with minimal guarding שמירה פחותה . Also, theגמרא says that according to ר' אלעזר that an animal that has already proven dangerous must be slaughtered and our משנה is referring to such a case. On one hand, I can see the point of the רמב''ן because the שומר שכר did a minimal amount of guarding but all שומריםshould have done the proper amount of guarding. so only the unpaid guard is not obligated to pay. however, it seems hard to understand. The reason I say this is the law of the תחילתו בפשיעה וסופו באונס חייב is referring to the paid guard שומר שכר. It cannot be the שומר חינם because in any case he is not obligated where he did minimal guarding. so, it must refer to the paid guard. But he is obligated in the ברייתא even though he did minimal guarding. so how can you decide from a case where he is obligated to pay, even though he did minimal guarding, to a case where he also did minimal guarding and yet say he is not obligated.