Nothing is unsportsmanlike about playing the game by its established rules...rules which both players can leverage equally. Moreover, there's no requirement to play by preconceived notions of how a game ought to play out thematically or otherwise. Great tactics are devised precisely by breaking conventions and shaking up the expectations of your opponent. If a tactic bothers you then it should be encouraged and explored in order to see how it impacts the game. Blocking doesn't inhibit the contest at all and, in fact, makes it more nuanced and competitive.So, blocking is not unsportsmanlike at all. It is really quite sporting.
Then you share with most others here in having no idea what sportsmanship means.
This stance makes no sense. It gives sportsmanship such a nebulous meaning that it has no meaning. The second you start wielding "sportsmanship" in an attempt to force your opponent to play the way you want them to play, as opposed to the way they'd like to play within the rules of the game you both agreed to play, you've taken a number of steps towards ruining both the game and the concept of sportsmanship.
This whole X is cheap phenomenon on these boards is just an attempt by people to exert social pressure to curtail legal play they seem to just keep getting beat by. They can't beat it in game so they try and convince others it isn't a legitimate way to play as to beat it from outside the game.
There is no reason, unless that is how the want to learn, to take the kid gloves off with a new player and relentlessly jam them with your ships in a casual game. Same could be said of barrel rolling out of every arc or dragging them around with Biggs. But you absolutely do have to introduce them to those game elements so they can learn what to expect, how to counter it, and how to utilize it themselves.
Otherwise you'll end up with another poster on here who calls tactics they have difficulty dealing with cheap.