Here are just a few things:
*The Cubs 56th overall pick came as compensation from Carlos Pena (the spacing around 43 and 56 got kind of messed up too)
*It is kind of a contradiction to say that Johnson has three good pitches and then say in the last sentence of the paragraph that he needs to improve the change in order to be an effective big league pitcher
*I don't like one sentence paragraphs. I would have added that he could be an effective reliever if the injury concerns reemerge or something to that effect. The sentence is also kind of awkward to me.
*I would make a change to the second sentence about Blackburn. I would change the phrase "and then" to "along with" to make it a little less redundant.
*You start a lot of sentences with subordinate clauses. That is fine to do some of the time, but you use it five times. Add in the two sentences you start with however and your writing lacks directness expected in this style of writing. I think you could write those 7 sentences more clearly and it would make your writing more dynamic.
Minor criticisms really, but you asked for suggestions.