The first question of chapter 21 is the timing of Jesus' "temple tantrum", a term I've never heard before, and while I don't think it's likely to catch on, it does have a ring to it. The Gospel of John clearly puts it at the beginning of his ministry, while the others put it near the end. There are two common interpretations of this discrepancy, the most common one being that this event happened twice, and John's Gospel tells the first time, while the others tell the latter. Another possibility (although this may be my own interpretation alone, as I can't recall specifically hearing this anywhere) is that John's Gospel is simply not interested in chronology, and specifically outside of the last week of Jesus' life, John simply strings together stories he remembers in any old order, which also explains why his Gospel is so different from the other three.
The next question is the manner of transportation that Jesus used to enter Jerusalem. There is definitely some confusion here, but note that while the other Gospels are arguing between a colt and an ass, the passage here in Matthew talks of "a colt the foal of an ass" which would indicate that the colt was an ass nonetheless. So that really leaves only Matthew that seems to be indicating Jesus riding on two animals. Since, as the SAB itself seems to be well aware, this is pretty much a physical impossibility, I would say that Jesus rode on the colt (a young ass) and perhaps the mare (if that's the right term) was brought along.
Anyway, all of this was supposed to fulfill a prophecy in Zachariah 9:9, but the SAB objects that this cannot be correct due to technicalities in the following verses, namely that Jesus failed to have an army or (an earthly) kingdom. This is the sort of technicality that never bothers Christians, though, I'm afraid, as there is an understanding that a future day is coming at which all of that will be completely fulfilled. There are actually a lot of prophecies that Jesus sort of half-fulfilled with an understanding that the complete fulfillment would come in the future. I'm sure most skeptics will call that sort of thing a cop-out once again, but I've got nothing else on this one.
Later in the chapter, Jesus famously curses a fig tree, but how fast did the curse take? In this telling of the story, it says "presently the fig tree withered away" while in Mark's Gospel, we're told "in the morning" they saw the "tree dried up from the roots". This could certainly be an outright contradiction, or it could be that certain members of Jesus' party noticed it at different times, or it could be that there's something else going on here which is a pure guess on my part: perhaps "withered away" and "dried up from the roots" could be different terms for stages of drying out that the tree passed through. I don't know enough Greek (or enough about figs) to say whether that has any deeper merit, I only toss it out as a possibility, as I recall there was a similar issue involved in drying of the ground after Noah's flood. (I think I've mostly been skipping the "What the Bible says about X" pages when they come up, but I think there's a quick note I could make about the fig page: All this destroying of fig trees is, I think a testimony of how good figs are rather than bad. After all, if you want to punish someone, you take away something good, right? You don't see God smiting their poison ivy or some such plant, do you?)
Jesus tells a parable of a rented vineyard in verses 33-41, and the SAB marks it with injustice and violence. I've got to ask, towards whom? I would agree that the people running the vineyard were unjust and violent, but I'm not sure that's what the SAB means, perhaps implying that "the lord of the vineyard" was unjust and violent for taking revenge on these men for killing his servants and son. If so, I can't really agree.
Last issue in the chapter is verse 44, which is marked as violent, unjust, and intolerant. That's a lot to pile on a bit of poetic language, as the stone spoken of is indeed Jesus, but that being so, what does the verse really mean? (After all, Jesus is not literally a stone.) I have my own thoughts, but barring an interpretation of what the SAB thinks it means, I'm not sure what to say.