The Pied Piper of Hamelin is a legend about a city in Germany that was overrun by rats, and the Pied Piper led them out of the city. When the government refused to pay him, the Piper played his enchanting tune and led all the children out of the village. (This is a very condensed version of the story, by the way.) Anyway, when someone is referred to as a Pied Piper, it means that they have some sort of appeal that makes people admire and follow them.
In cities and urban areas (in the U.S.), intersecting streets divide areas into "blocks." If someone lives on your block, that means they're your neighbor. If someone is referred to as "Ziggy on the block", it means that Ziggy grew up in the 'hood (neighborhood), or is an urban person. If someone is described as "the new kid on the block," it means someone who has just moved into your neighborhood.
To hit the wall means to suddenly stop, to run out of steam or energy. It can also refer to encountering an insurmountable problem.