Piggy is considered to be an outcast among the group of boys because of his overweight appearance and poor physical condition. Unlike the other boys on the island, Piggy wears glasses and refuses to participate in physically challenging activities because of his asthma.
In addition to Piggy's poor physical condition, he is rather annoying and continually attempts to voice his opinion. Piggy also supports Ralph and is a proponent of civility, which is something that further distances him from the majority of the group once Jack begins to gain influence. Piggy is also not afraid of confrontation and continually criticizes the boys for their disobedience.
Piggy's overweight physique also makes him the subject of many jokes, and the boys also probably resent his intelligence. Overall, Piggy is an unpopular child, whose continual criticism of the boys' savage behavior during their stay on the uninhabited island marks him as an outcast.