That’s true, pokeplayer, but another fact about carnivores is that they generally prefer to hunt prey that they can kill easily and quickly, with the least risk of injury to themselves. This translates to young, old, and weak animals being the preferred targets of most predators. (I know of one scientific paper that suggests that carnivorous dinosaurs mostly fed on young prey that they could swallow whole, thus explaining why the bones of juvenile dinosaurs, and evidence of attacks on large dinosaurs, are so rare in the fossil record.) Not only does the gang fit the bill for an (apparently) easy meal from most sharpteeth’s perspectives, but usually, when the gang is attacked by sharpteeth, they are in the Mysterious Beyond or some other place where there does not appear to be a great deal of alternative prey; therefore they become the easiest available prey by default.
Furthermore, despite what you might see on nature documentaries (though the statistic may sometimes be invoked by the narrator), most of the time a hunting predator fails to catch its intended victim. I’ve heard that the success rate for polar bears catching seals is 1 in 20, and something like 1 in 25 for tigers hunting deer. Things probably weren’t much different with dinosaurs; there are, in fact, a number of fossils of herbivores that were bitten by a predator, and not only escaped, but survived long enough to heal. In short, it’s not just natural, but necessary for predators to make repeated hunts.
Granted, most predators probably don’t concentrate their repeated efforts on the same prey each time, but I don’t think they usually bother to keep track of which animals they’ve stalked before. If, by coincidence, a leopard happens upon the same antelope it failed to catch on a previous hunt, there’s no reason for it to pass it up if it has a second chance at a successful kill. And in LBT, when the gang is often the only apparent prey in the vicinity (and generally not very good at remaining inconspicuous), situations like this are virtually guaranteed.
In the first movie, the gang is just about the only prey available for Sharptooth to hunt, and they are headed in the same direction as him (though Sharptooth’s motive is to follow the migrating leafeaters that are his food source), so it’s not surprising that their paths cross repeatedly.
In LBT II, Chomper’s parents presumably entered the Great Valley because they were searching for their son, and it’s likely that they attacked the gang because they happened to be in the way. Chomper’s mother’s confrontation with Grandpa Longneck is a bit of a mystery, since we didn’t see how it started. She may have seen him first, and attacked him on the assumption that he would be easy prey. However, considering that Littlefoot’s grandparents had heard the sharpteeth beforehand, I think it’s also possible that Grandpa Longneck attempted to drive Chomper’s mother off, leading her into the water to gain an advantage. (Or she might have run into him while he was on his way to warn the other adults, in which case wither or both hypotheses might be true.)
In LBT III, the raptor pack is faced with a choice of prey: a band of well-armed full-grown dinosaurs clearly intent on fighting them (Mutt’s father notwithstanding), or a group of fleeing youngsters accompanied by a lone adult
Hypsilophodon. Later, when the adults are unconscious and utterly defenseless, the raptors clearly intend to eat them, completely ignoring the gang. Things get a little chaotic (with the raptors’ apparent choice of targets switching back and forth) after Hyp’s father joins the fray, Hyp basically invites the raptors to chase him, the adults wake up, and the gang starts pushing rocks down on the raptors, but ultimately the raptors appear to lose interest in the gang, and are advancing on the adults at the time the dam breaks.
Chomper himself says in LBT V that there isn’t much to eat on his island, so it’s not much of a surprise that the
Giganotosaurus chooses to go after the gang. (His attack, furthermore, is really just one prolonged chase, and he probably would have succeeded in catching the gang had it not been for Chomper’s parents’ intervention.)
While the LBT VI
Allosaurus did not come off as an especially competent hunter, getting his head stuck between two trees, making a point of waiting until every member of the gang (even an uncharacteristically oblivious Cera) notices him before attacking, and missing Spike and Littlefoot by a mile to take a bite out of a log and send himself plummeting into a canyon, there again isn’t much indication that he has a lot of prey to choose from. And when he wakes up from his fall to find a small longneck
inside his mouth, is it any surprise that that’s what he chooses to go after? Later, both the
Allosaurus and the
T. rex who unexpectedly shows up concentrate their predaceous efforts on Grandpa Longneck, paying no attention to (or possibly not noticing) the kids gathered rather conspicuously nearby.
The repeated attacks of the LBT VIII sharptooth can probably again be justified by the fact that it didn’t have a lot of prey options, and four young leafeaters with an elderly
Pachyrhinosaurus appeared to be an easy target. (The nearest alternative that we know of was the spiketail herd, whose members were predominantly fully grown and probably accustomed to encounters with sharpteeth.)
The
Liopleurodon in LBT IX seemingly tracked the gang down for a second attempt at catching them after it failed the first time, but again I don’t think it was doing this out of villainy. The first time it attacked them, it was in a landlocked pool where the only available prey was a single, similarly trapped ichthyosaur: probably not optimal living conditions from a giant seagoing predator’s perspective. Even though Mo was right there at the time of the attack, he was a less substantial meal (probably harder to catch as well) than the five
Liopleurodon-naÔve locals waiting within grabbing distance at the water’s edge. Later, after escaping from the cave the earthshake had trapped it in, the
Liopleurodon would have found that there was no prey in the pool at all (apart from several inconsequentially small fish), and, like any animal that finds itself in a territory lacking in sufficient food, moved on to find more, leaving through the same outlet which Mo and the gang had taken. Considering that there were implied to be multiple streams that could have potentially led to the Big Water (the gang’s reason for sending Petrie ahead to scout), but the
Liopleurodon still ended up at the same spot as the gang, it’s not impossible that it
was following them (probably by scent). However, it’s likely that it was specifically tracking Mo, who, having also come from the Big Water, would have provided a familiar scent that the
Liopleurodon would have been naturally inclined to follow. I think the second attack was a case of the gang simply being in the wrong place at the wrong time. And judging from Mo’s story afterwards, after the
Liopleurodon lost track of him, it completely forgot about food once it smelled its home close by.
Most of the sharpteeth that appeared beyond LBT IX suffered too much from “incompetent predator syndrome” to come off as villains OR realistic predators, in my opinion. The LBT X sharpteeth were embarrassingly bad hunters, to say the least, and demonstrated no teamwork to speak of (each going after a different adult longneck rather than ganging up on a single individual). They were at least smart enough to limit their attacks to a few scattered longnecks and several young dinosaurs, rather than go after the massive conglomerate herd in the crater, but even after all of them had taken more tumbles and pratfalls than The Three Stooges in a floor wax factory, they still tried to chase Bron up the slope (until they were frightened off by the eclipse

).
The two raptors in LBT XI seemed to be very prone to distraction and poor judgment (namely, attacking Mr. Threehorn head-on

), as well as the disconcertingly common LBT predator handicap of taking
forever to strike at times.

Again, however, I din’t think they were so much villainous as suicidally hungry.

While the LBT XII
Spinosaurus seems to have forgotten that essential step in the feeding processóswallowingóhe does seem to follow the predatory convention of attacking the most convenient and nutritionally rewarding prey. As soon as he notices Spike, Cera, Littlefoot, and Ducky, he loses interest in the much less substantial meal offered by Petrie and Guido. Even when the two attempt to distract him, he only momentarily snaps at them, and then, after they fly out of range, continues chasing the others. Actually he is probably most unrealistic in the amount of time he spends pursuing the gang, probably burning at least as many calories as he would gain from eating them.
Finally, the four
Baryonyx in LBT XIII may have been unusually persistent in pursuing their intended prey, but considering the identity of the prey in question, it could be argued that they were pursuing the Holy Grail of easy meals.

In my opinion, Red Claw (and by extension, Screech and Thud) is the only sharptooth in the series who could potentially be considered a villain. Judging from Ruby’s story in “The Meadow of Jumping Waters”, in which she states that Red Claw was trying to stop her and Chomper from reaching the Great Valley, it appears that he may be specifically after the gang (perhaps mainly Ruby and/or Chomper) for some reason. In at least two episodes he has made a deliberate attempt to break into the Great Valley, despite the fact that he probably wouldn’t last long there before being driven out. Unfortunately, we know so little of his backstory that it is hard to say what his motives are.