RO #47 -- Other (Slipped Pattern, and amplification): Note that this could be fixed in a variety of ways: Perhaps the worst thing to do is to make the student simplify: "There are many kinds of tricks. The sweeper and the boneless are the most popular." Subordination would work: "There are many kinds of tricks like the sweeper and the boneless, which are the most popular." The "like" suggests that amplification with a dash would best fit the writer's meaning. "Tricks" is a general term; the "sweeper and the boneless" are specific examples: "There are many kinds of tricks -- the sweeper and the boneless are the most popular."
RO #48 -- Contrast: If we assume that the run-on reflects not just a sloppy error, but rather some logical relationship which the writer had in mind but did not know how to convey, then there is certaainly a contrast between going up and coming down: "They have a half pipe in which you ride up one side and do a trick; then you come down the other side."
RO #49 -- Subordination (or amplification): This appears to be a cause/effect relationship, although it could also be seen as amplification: "Most skateboards are not fit to be ridden because they have truck brakes [?] which might break on you." or  "Most skateboards are not fit to be ridden -- they have truck brakes [?] which might break on you."
RO #50 -- Amplification (or sloppy):  This could be a sloppy error. A period would work here. But these are the only two clauses on the "birdie" before the writer goes on to the "reply sticks." Thus the second can be seen as providing more details on the first. "Then you have what is called a birdie, which will raise you up on to the sidewalk -- it only costs $6.99 on sale." Subordination would have worked, but it would have resulted in a 23-word main clause. "Then you have what is called a birdie, which will raise you up on to the sidewalk and only costs $6.99 on sale." The longest main clause in the passage, however, is 22 words long, and the writer's average is 10.8.
RO #51 -- Subordination (Slipped Pattern):  This may be the result of a stretch for more subordination: "Then you have [RNDOwhat is called reply sticks [RAJFwhichare the best pair of rails [RAJFyou can get for a skate board.]]]" This version, however, includes a third level embedding of a clause, in a 22-word main clause, which might be too much of a stretch for this student. If the student were taught how to analyze the syntax of his own writing, he would have found the problem with the subject of "are," and would probably have opted for the simpler version: "Then you have [RNDOwhat is called reply sticks.] Theyare the best pair of rails [RAJFyou can get for a skate board.]" On the other hand, the student might have understood and preferred the level three embedding. The KISS Approach enables students to understand and control the sytax of their own writing.
RO #52 -- Subordination (and length):  My guess is that the writer meant "Reply sticks are the best pair of rails you can get for a skate board because they help the birdie get you up on the sidewalk." The main clause, however, had already been messed up. (See RO #51.) Without a clear main clause to which to attach the subordinate idea, the writer simply wrote the content and omitted the logical subordinator.