I’m guessing most of you don’t feel like re-watching the carnage that happened over the past few days, but not to worry: I hated myself enough to review what happened. You can thank me with gift baskets. Now let’s talk about how awful Boston’s defense has been before I go back to banging my head painfully against the corner of a cabinet.There’s been a common theme —a rather strange one, in fact — in all of the last three Celtics losses. Of course, the same problems still exist: rebounding, transition defense, inconsistent jump-shooting, etc. That never changes. But against Los Angeles, Golden State and Sacramento, the Celtics have been playing particularly awful defense on one set in particular: spot-up opportunities.Let’s begin with Thursday’s torture-porn matchup against the Clippers. The Celtics ran headlong into a buzzsaw against LA, catching a very hot, very good team at exactly the wrong time. Unsurprisingly, the Clippers took it to the Celtics in transition, destroying Boston with 1.5 points per possession in the open floor. But the Clippers took a LOT of spot-up shots. 26.4% of all Clipper possessions ended in a spot-up attempt, and in those opportunities, the Clippers averaged 1.13 PPP. By way of reference, the Warriors (and we are getting to them) are the best spot-up team in the NBA, averaging 1.1 PPP. So in a ton of spot-up attempts, the Clippers produced more points per possession than the average of the best team in the NBA, .08 PPP more than the Clippers themselves average for the season..08 PPP is a noticeable difference to be sure, but one could make the argument that it was simply a good shooting night for the Clippers in a vacuum. But the NBA doesn’t exist in a vacuum, and the context of the Clippers game is important if we examine the two games that followed.As we mentioned before, Golden State is literally the best spot-up team in the league. On Saturday, 25% of Golden State’s possessions were spot-up attempts. This isn’t out of the ordinary. A team with talented shooters like Steph Curry and Klay Thompson — as well as stretch bigs like David Lee — will take a lot of jumpers and hit a lot of jumpers. But the Warriors hit a LOT of jumpers Saturday night — more than can be explained away by simple good shooting. In spot-up opportunities, Golden State averaged 1.6 points per possession. Read that again: the Warriors averaged 1.6 PPP. That’s .5 PPP more than they average overall in spot-up situations, and it happened in a very large one-game sample size.Now, again, the Warriors are very good shooters and they deserve plenty of credit for knocking down a variety of shots. But Boston’s defense on spot-up sets was disturbing on several different levels. The first and most apparent level was in the way they contested jumpers. Observe:So much is wrong with Brandon Bass’s defense here. SO much. When David Lee gets the pass, he is out of his range at the top of the key, and Bass is defending the mid-range jumper that Lee can hit pretty consistently. But when Lee steps up, Bass doesn’t react. Instead, he remains exactly where he is with his hands down.Bass seems to have given up this play as a lost cause, making one wonder why he didn’t just start off closer to Lee to begin with. Plays like this made the Golden State game almost unwatchable. At times, it seemed that the Celtics were engaged and contesting shots on defense (mostly during their brief third and fourth quarters runs), but for the vast majority of the game, Boston sat back and watched as the Warriors poured in jumpers.Even when the effort was there, the Celtics looked a step slow.Pierce made the correct decision chasing Barnes off the 3-point line (and really, did Collins not get to his spot on time? That looks like a charge, no?), but part of the problem with that play is that Pierce and Collins are trying to defend Harrison Barnes who was presumably still reading Captain Underpants comic books when Collins and Pierce began their NBA careers. Still, at least early on shots were being contested and defensive rotations were in place (that was a damn charge).Later in the game…well. The rotations may have degraded a bit.Here’s my defense for Courtney Lee: Jarrett Jack was 1-9 up until that point, so helping off him might not have seemed like a particularly dangerous decision. Here’s the rather obvious counter: The Warriors were shooting roughly 800,000% from 3-point range and had scored just 0.27 PPP in the post. So the rotation really made no sense and speaks to the unfortunate lack of awareness the Celtics displayed all evening. Even if Lee thought he was going to get a trap steal from behind, he needed to recognize the bigger offensive threat and adjust accordingly.But he didn’t. Jarrett Jack got the ball, knocked down a 3-pointer to get himself on track and finished off the Celtics in the following possessions. This brings us to the second, more disturbing level we mentioned earlier. The Celtics were bad, certainly, and the Warriors were great, obviously. But the Warriors were great in sets where they are usually great. They hit jumpers, and they used those made jumpers to create spacing problems when Boston chased them off the 3-point line. But how did the Celtics not see this coming? Anybody who watches the NBA could tell you that Golden State is going to hit jumpers. But allowing them to hit EVERY jumper on EVERY possession is simply allowing a talented team to play to their own strengths entirely too much.Which brings us to Sunday’s abomination against Sacramento. Let the record show that though the Kings are a fairly bad team, they are fine in spot-up opportunities (1.06 PPP in 18% of their possessions, 7th in the NBA overall). But the Celtics allowed Sacramento to average 1.64 PPP in spot-up attempts. That’s a difference of 0.58, which is an unbelievable differential. How could this happen?What’s interesting (and somewhat telling) is that the Kings actually started off cold. In their first 10 spot-up attempts, the Kings were 2-10 from the field. In their final 12 attempts, they were 11-12, including 7-7 from 3-point range. And once again, much of Sacramento’s success was due to Boston’s lack of attention on defense. I don’t mean to pile on Courtney Lee (who I honestly believe has been improving over the past few weeks), but the shoe fits unfortunately.Stop me if you’ve heard this one before: Lee gambles unnecessarily on a player who is pretty well covered already. Lee’s defensive assignment shifts slightly and gets an open 3-pointer as a result. Lee gives up crucial 3-pointers to open opponents.The strange thing is that even after the past three games, the Celtics are 11th in opponent PPP in spot-up opportunities, allowing just 0.94 overall. So even after three consecutive games in which they gave up unreasonably high levels of efficiency, the Celtics are still above average. This isn’t a good thing. It means that the Celtics were, at one point, a good team defensively on spot-up shots but are quickly falling off into something much less good. Something is very wrong with this team, and it has been noticeable in the past week.Is this a strange anomaly? A coincidence? A sign of something more troublesome? It’s difficult to say. Whether it speaks to a lack of preparation on Doc’s part or Boston’s effort and execution (or some combination of all of those things) really isn’t clear, but in any case, it’s not a good sign. Good teams (like Golden State and Los Angeles) can beat you with their best play sets. That’s normal. But allowing them to DESTROY you speaks less about their success and more about Boston’s general defensive malaise. That malaise will have to lift VERY soon if the Celtics want to salvage this season.Follow Tom on Twitter: @Tom_NBA.