The tribe of savages steals Piggy's glasses from Ralph. These glasses are used to start fires in the story.
In William Golding's novel "Lord of the Flies," it is Jack's group of savages who accompany him to steal fire from Ralph's camp. They violently attack Ralph and the other boys to steal the fire and assert their control over the island.
Well in chapter 10 Jack and his tribe of savages invade Ralph's tribe (made of up Ralph, Sam and Eric, Piggy, and one/two littluns) in order to steal Piggy's glasses, which is overall the power to start a fire on the island. Jack might have mentioned this plan in chapter 9 so I'm hoping this is the right answer to your question.
He wishes to remind Jack and his tribe that they are really just English schoolboys and not a tribe of murderous savages.
To get Ralph out of the tangled undergrowth, the savages smoke him out by setting the jungle on fire.
Ralph wanted Piggy, the twins and himself to tidy up and wear their clothes, hoping by doing so he could remind Jack and his tribe that they weren't really a tribe of savages at all but simply English schoolboys.
Ralph says, "Suppose we go, looking like we used to, washed and hair brushed... After all we aren't savages really and being rescued isn't a game." When Samneric point out that Jack and his tribe will be painted Ralph replies, "Well we won't be painted... because we aren't savages."
They took Piggy's glasses, and fire from Ralph's camp.
Ralph say this when he has called his last meeting and is talking to Samneric and Piggy. When he mentioned going to confront Jack and his tribe at Castle Rock he said that they should go as they were. Samneric pointed out that Jack and his tribe would be "painted up" to which Ralph replied, "well we won't be, we're not savages and being rescued isn't a game."
In the noun phrase 'a tribe of savages', the noun tribeis functioning as a collective noun.
One important example of this 'protecting' as you say, is after Piggy dies and Ralph is alone. Sam and Eric are tortured and forced into joining Jack's tribe and they are guarding the pathway up to Castle Rock. Ralph sneaks up and talks to Samneric (as they are referred to) Apart from that important conversation the savages usually protect the entrance with their spears. Two savages at a time. Samneric are scared, 'gibbering' as Golding writes, and Samneric are new to the tribe so they either don't want spears, or Jack doesn't trust them. Hope it helped :)
He hope to remind Jack and his tribe that they are not savages but simply schoolboys stranded on an island. He hope that this will remind them that they are civilised human beings and that there are some things that they should not do.
Samneric continue to show loyalty to Ralph by warning him about the plans of Jack and his tribe, providing him with information about what is happening on the island, and ultimately helping him when he is in need. Their loyalty to Ralph is tested, but they remain committed to him throughout their ordeal.