Oi, oi, oi!
And it came to pass that punk was born. And it was good. But as the first wave continued on, certain members of the scene began to believe the new members were intellectuals adopting the scene for credibility and glamour, trying to divorce the scene from its roots. While there's certainly nothing wrong with intellectual punk, there was a drive for music that reflected the everyday struggles of the working class.
Thus was born Oi! (yes, the exclamation point is mandatory). Taking the early wave of punk typified by the Sex Pistols and the Clash and blending it with older influences such as pub rock, folk, and ska, Oi! focused on topics such as workers' rights, the welfare state, and issues with cops and the government. The genre appealed to punks and skinheads alike, but came to be known as the genre of skins. And like the skins themselves, Oi! had associations with racism - we're looking at you, Skrewdriver - but a good chunk of the scene stayed away from that shit. As it says on the main page for Punk Rock, there's a decades-long struggle between the fascist sub-elements of Oi! and the apolitical and stridently anti-fascist elements of the scene that will likely be resolved some time after the sun goes out.
And out of Oi! came street punk. While borrowing many of the aspects (such as sing-along choruses) and working class concerns of Oi!, street punk spread out to cover other aspects of city life, such as relationships, drinking, violence, and the turmoil of the urban jungle. Street punk was also more stridently political, stretching out beyond working class concerns into (typically) either a left-leaning activism or a "We're all fucked up" outlook. In contrast to the more straight-laced image of Oi!, street punk glorifies in the more outlandish imagery of the scene - multi-colored mohawks, spiked jackets and vests, and clothing covered with patches for bands and political causes. See also Folk Punk.
Bands associated with Oi!:
Band associated with street punk: