On the other hand I'm pretty sure hunters get them before they get that big.
Hunting boar can be really difficult. They have much better senses than humans and they travel in packs with lookouts that alert the rest of the pack to danger. They are very shy and scram as soon as they see, hear, or smell a human coming. Making things even more difficult they usually hide and sleep all day coming out to eat at night. They also breed like rabbits, a single sow can have 16 offspring a year, roughly half are female. After a year each one of those females are ready to have 16 offspring of their own. So if the populations aren't kept in check they can grow explosively and when they do they absolutely devastate local agriculture.
The are however some effective ways to hunt them. You can use a large group of hunters and dogs to drive the pack of boar towards a set of waiting hunters. Shooting them in this type of hunt requires significant skill since the boars come running full speed through the forest and you have less than a second to see if the boar in question is OK to shoot, meaning it's not a sow with young offspring. This type of boar hunt is common in Europe but since it requires loose dogs chasing down the boar it's pretty tightly regulated. https://www.youtube.com/watch?v=7ob0fgc0I7A
You can stalk boar in the dusk and the dawn when they come out to eat. This can only be done in certain wind conditions but it can be very effective if the hunter is skilled enough. https://www.youtube.com/watch?v=HP15acQzsp0
There's an Australian method of culling them by driving around farmland with an ATV, dirt bike, or 4x4 shooting anything that gets scared out by the ATV. This requires quick shots on moving targets but it's usually very effective. However often the pigs aren't taken care of, they're just left to rot. So I wouldn't call it hunting. https://www.youtube.com/watch?v=nTpTIVlC7Ho
Finally there is a US method of eradicating them which is simply shooting them from a low-flying helicopter. This can be very effective, it was used to wipe out the goats that were plaguing the Galapagos islands. This method is also more eradication than hunting, and is usually used to eliminate pig populations on large farms where the pigs to massive damage to the crops. https://www.youtube.com/watch?v=nV_d0IMJ_tk