Assalaamu `alaykum
The hadeeth is referring to the Khawaarij, who are from those whom the Prophet :saw2: talked about and their description. They are the ones who fought the Sahaabah, rebelled against the Muslim rulers and applied the verses of Allaah regarding the kuffaar on the believers.
Lets break the hadeeth you posted in two:
"During the last days there will appear some young foolish people who will say the best words but their faith will not go beyond their throats (i.e. they will have no faith) and will go out from (leave) their religion as an arrow goes out of the game."
This is referring to their descriptions and the type of people they will be. There is already a thread about the khawaarij that akhee Mabsoot opened:
http://www.turntoislam.com/forum/showthread.php?t=49414
"So, where-ever you find them, kill them, for who-ever kills them shall have reward on the Day of Resurrection."
Here are a few points of benefit that I got from the explanation of this hadeeth in Saheeh Muslim by Imaam al-Nawawi:
- It is obligatory to fight against the rebellious khawaarij.
- There is an Ijmaa` (Agreement of scholars) regarding the obligation of fighting against the rebellious khawaarij. This is what Imaam al-Nawawi mentioned and Al-Nawawi quoted Qaadi `Iyyaad statement regarding the Ijmaa`
- It is not only the Khawaarij that are obligatory to be fought with but the people of innovation who rebel against the Imaam and oppose the view of the Jamaa`ah and broke away from it. This is what Al-Qaadi mentioned as quoted by al-Nawawi
- It is obligatory to fighting them after warning them and making excuses for them. Mentioned by Al Qaadi.
- If they do not rebel against the Muslim ruler nor start war against the Muslims, then they are not to be fought against.
The evidence for fighting them:
"...But if one of them oppresses the other, then fight against the one that oppresses until it returns to the ordinance of Allah...."[Soorah al-Hujuraat: 9]
They are oppressors because:
- They rebel against the Muslim rulers causing mischief in the land.
- They fight against the Muslims.
- They make takfeer of the Muslims.
Obviously, it should be noted that the establishment of war against the khawaarij is the role of the Muslim ruler and not individuals. This is what the Sahaabah did under the khilaafah of `Alee radiyAllaahu `anhu, who fought the khawaarij.