Joe La Boot is a retired baseball player who dropped an easy catch a long time ago.
People still seem to remember it, like Grampa who hated him for it. Lisa took Bart to see him after Bart too dropped an easy catch. Once La Boot talks to Bart, he suddenly realizes who Bart is and notices that Bart's drop is much worse than his drop, thus making him insult Bart and encouraged everyone nearby to do the same. But later, when Bart attempts suicide by jumping off of the water tower while everyone else is egging him on, La Boot (perhaps regretting his actions and seeing a chance to redeem himself) tries to catch him, only to miss. Grampa immediately shows up and tells La Boot that he sucks.