Why the Rashbam deviates from peshat in the shattering of the luchot

Here is a 30 minute shiur by Rabbi Barry Gelman on parshat Ki Tisa, from 2011:
What I Learned From My Principal and my Basketball Star Friend: How Could Moshe Break the Luchot


He focuses in large part on Rashbam, who says that Moshe didn't break the luchot in anger. Rather he lost strength and pushed them away from himself so that they would not fall on his feet. And that seems to go against the peshat, that Moshe was angry, as it says immediately before. And also while accounting for וַיַּשְׁלֵךְ מִיָּדָו, it doesn't account for וַיְשַׁבֵּר אֹתָם.

Here is the pasuk (Shemot 32:19):

יט  וַיְהִי, כַּאֲשֶׁר קָרַב אֶל-הַמַּחֲנֶה, וַיַּרְא אֶת-הָעֵגֶל, וּמְחֹלֹת; וַיִּחַר-אַף מֹשֶׁה, וַיַּשְׁלֵךְ מִיָּדָו אֶת-הַלֻּחֹת, וַיְשַׁבֵּר אֹתָם, תַּחַת הָהָר.

19 And it came to pass, as soon as he came nigh unto the camp, that he saw the calf and the dancing; and Moses' anger waxed hot, and he cast the tables out of his hands, and broke them beneath the mount.

and here is Rashbam:

פסוק יט 
וישלך מידיו - כשראה את העגל תשש כחו ולא היה בו כח להשליכם רחוק ממנו קצת שלא יזיק את רגליו בנפלם, כדרך כל משליכי משאוי כשאין בהם כח לשאת. 
וכן ראיתי בפרקים של רבי אליעזר ועיקר פשוטו כך. 

"When he saw the eigel, his strength weakened and he only had sufficient strength to throw them a short distance from himself so that they would not hurt his feet as they fell, in the same manner of anyone who casts away a burden that they don't have strength to carry. So I have seen in Pirkei deRabbi Elizer, and the primary peshat is like that."

Now for my disagreement, and defense of the Rashbam:

We don't have to agree with Rashbam in his assessment that this is peshat, but I would argue that he is being honest here, rather than trying to defend/cover up Moshe's extreme actions. He is straightforward in his approach to peshat and even if we don't understand Rashbam at first, we should consider (a) contextual information and (b) implications of phraseology, and how words are used across Tanach. After all, he acknowledges the midrashic source but also indicates that he considers it to be the primary peshat.

A) For instance, וַיִּחַר-אַף מֹשֶׁה, וַיַּשְׁלֵךְ מִיָּדָו אֶת-הַלֻּחֹת seems to draw a pretty direct connection between the two.

However, #1, where do you want to put the esnachta? As written by the author of the trup, it is:

וַיְהִי, כַּאֲשֶׁר קָרַב אֶל-הַמַּחֲנֶה, וַיַּרְא אֶת-הָעֵגֶל, וּמְחֹלֹת
etnachta
וַיִּחַר-אַף מֹשֶׁה, וַיַּשְׁלֵךְ מִיָּדָו אֶת-הַלֻּחֹת, וַיְשַׁבֵּר אֹתָם, תַּחַת הָהָר

However, as shown elsewhere, Rashbam does not consider trup to be dispositive, so he could perhaps move the esnachta:

וַיְהִי, כַּאֲשֶׁר קָרַב אֶל-הַמַּחֲנֶה, וַיַּרְא אֶת-הָעֵגֶל, וּמְחֹלֹת, וַיִּחַר-אַף מֹשֶׁה
etnachta
וַיַּשְׁלֵךְ מִיָּדָו אֶת-הַלֻּחֹת, וַיְשַׁבֵּר אֹתָם, תַּחַת הָהָר

This seems a but forced, especially since Moshe is named explicitly, as if introducing a new half-pasuk and serving as the explicit antecedent for all the pronouns which follow.

But, #2, Rasham tagged Pirkei deRabbi Eliezer as his source. So to understand how he parses the pasuk, and  וַיִּחַר-אַף מֹשֶׁה, maybe we should first examine the midrash and see how it understands and explains Moshe's anger, and at the same time says he was merely casting it off.

This midrash may be found in Pirkei deRabbi Eliezer, perek 45.

That is that the words carried themselves and Moshe will them, and when they (!) "saw the eigel and the dancing" the writing fled from the luchos and they were too heavy upon his hands, and Moshe was unable to carry either himself or the luchos, and he cast them from his hands and they were broken at the bottom of the mountain, as is written "and his Moshe's anger waxed... and he broke them at the bottom of the mountain."

OK, that doesn't help much. Depending on which girsa, perhaps the anger is elided, or perhaps not. (See gloss, insertions.)

On the basis of this, though, maybe we can see what Rashbam is suggesting.

וַיִּחַר-אַף מֹשֶׁה is definitely there in the pasuk. But we can say that he had an emotional reaction. Speaking from personal experience, under extreme emotion, it is sometimes difficult to contain yourself. I would guess that Rashbam, rather than asserting miraculous carrying of the luchos, is simply saying that when Moshe saw the eigel and the conduct of the people, he had an emotional reaction. And this physically weakened him such that he could no longer carry the luchos, and so naturally, he was in danger of dropping them on his feet.

B) What about וַיַּשְׁלֵךְ מִיָּדָו, which is a hiphil (causative). See here for uses of it across Tanach. It could be understood as flung.

But Rashbam agrees there was a forceful push here. Maybe he is focuses on the word מִיָּדָו, that he cast it from his hands (implying just from his hands, a push of a short distance), rather than that he threw it down in anger towards the bottom of the mountain.

C) What about וַיְשַׁבֵּר אֹתָם תַּחַת הָהָר, also active and causative? This can be understood as that, as a result of casting them from his hands, thus, he ended up causing them to break at the bottom of the mountain, since they dropped there. But this is not direct and deliberate breaking, but rather the ונתשברו of Pirkei deRabbi Eleizer. He caused this event indirectly by dropping them, or pushing them from his hands.

D) Maybe he considers narrative context, that Moshe already heard that they had sinned and was still carrying down the luchos to give them. One could posit a change of mind when directly witnessing the sin and its extent, but maybe Rashbam thinks this unlikely, and would rather keep Moshe consistent in his approach, and attribute the breaking to emotional accident.

In sum, while we may disagree with Rashbam, rather than consider this a strange deviation from peshat, I would rather say that he sees certain cues textual cues, both from narrative context and from close reading of phrases in the pasuk.