With that kind of crack, the best you can do is to disassemble the legs (Or with that specific figure, just unscrew the entire upper legs and knee to get the red part out) and carefully glue the cracked area with either super glue or poly-cement plastic cement; Wait for the glue to completely dry and cure, sand the excess dried glue, then reassemble everything together. For plastic cement, Plastic cement is best used for plastic on plastic contact. Plastic cement is basically acid and when in contact with the plastic, it is melting the plastic so that when you join 2 pieces they are fusing to each other over time; making 2 halves into a single solid plastic piece. This is great for eliminating seamlines after a good sanding, getting rid of tiny stress marks, or fixing cracked pieces. However, plastic glue also takes much longer to fully cure (~30min) than your standard super glue. Sometimes though plastic on plastic contact is not possible and that is when superglue comes into play. If you are combining porous materials such as cloth, metals, or magnets that is when you want to break out the superglue. Superglue does not really 'melt' what you are combining, it is more of a binding agent that hardens when it dries. As such it is much harder to shape, sand, and mold after drying if that is what you require of your model. It is also super strong but also super brittle. An accidental 'whack' at a particular piece with a proper amount of force and that thing is falling off. The most ideal way would be to fuse the crack with plastic cement, reinforce the fused crack with tiny daps of superglue after the plastic cement is fully cured, wait for fo the glue to fully cure, sand away any excess dried glue residues, then reassemble everything.