'Hybrid vigor', you're doing it wrong! This is absolutely NOT an example of hybrid vigor. First, we need to understand what 'hybrid vigor' means: heterosis, where the combination of genes from each parent results in enhanced fitness. Also see heterozygote advantage. (Read the damned links, please. At least skim, because I’m a dog breeder and I encounter a lot of ‘misunderstandings’ [read: bullshit] about what hybrid vigor IS. Yes, heterosis exists in dogs, no, hybrid vigor does not ONLY occur in crosses between species.) This liger is not an example of hybrid vigor, but of outbreeding depression, when the traits from the parents are not compatible and produce reduced fitness. The reason that ligers get so big is because lions are competitive breeders, a lioness may breed with more than one lion, so it is advantageous for the male to have genes that promote the growth of his offspring, bigger and faster than the offspring of other males the lioness may have dallied with. This is not an advantage for the lioness, so she has genes that will level the growth playing field so all of her offspring get an even start. When you breed a male lion to a female tiger, things change because tigers do not mess around, the whole litter is sired by only one male. So the female tiger has no genes that say, “yo, you are not going to get huge, little cub.” So the offspring grow, grow, grow.
This page has some interesting commentary on growth dysplasia in ligers, and some other competing hypotheses.
This animal is also grossly obese.