The Seeker is key to winning a game of Quidditch. If your team doesn't have a Seeker and the opposing team does, then the opposing team can only ever lose by surrendering. Unless there's a huge skill difference between the two playing teams, this is as good as an automatic win. It follows that if you have a strategy that can remove the opposing Seeker from the game for a long period of time, you should use it. In other words, if you can foul the opposing Seeker without significant losses, you should.
Put simply, my problem is that the books appear to show this outrageous tactic as being perfectly legal. For example, chapter 13 of Harry Potter and the Prisoner of Azkaban has Wood outright recommend it:
“HARRY, THIS IS NO TIME TO BE A GENTLEMAN!” Wood roared as Harry swerved to avoid a collision. “KNOCK HER OFF HER BROOM IF YOU HAVE TO!”
and chapter 11 of Philosopher's Stone as good as proves that a player can't be removed from the game as a consequence of fouling. Indeed, the punishment in this case was just a free shot at the goal posts.
Madam Hooch spoke angrily to Flint and then ordered a free shot at the goal posts for Gryffindor. But in all the confusion, of course, the Golden Snitch had disappeared from sight again.
Down in the stands, Dean Thomas was yelling, “Send him off, ref! Red card!”
“What are you talking about, Dean?” said Ron.
“Red card!” said Dean furiously. “In football you get shown the red card and you’re out of the game!”
“But this isn’t football, Dean,” Ron reminded him.
Hagrid, however, was on Dean’s side.
“They oughta change the rules. Flint coulda knocked Harry outta the air.”
Finally, chapter 15 of Prisoner has an extremely dirty game of Quidditch played, but the only punishments that I can see are more free shots at the goals. For example:
“That will do!” shrieked Madam Hooch, zooming between them. “Penalty shot to Gryffindor for an unprovoked attack on their Chaser! Penalty shot to Slytherin for deliberate damage to their Chaser!”
Bole hit Alicia with his club and tried to say he’d thought she was a Bludger. George Weasley elbowed Bole in the face in retaliation. Madam Hooch awarded both teams penalties, and Wood pulled off another spectacular save, making the score forty-ten to Gryffindor.
“YOU DO NOT ATTACK THE KEEPER UNLESS THE QUAFFLE IS WITHIN THE SCORING AREA!” she shrieked at Bole and Derrick. “Gryffindor penalty!”
are the only punishments that I can find, despite this being obviously deliberate damage. So why not foul the Seeker as much as possible?
In summary: Fouling the opposing Seeker is as good as an automatic win and the worst punishment for fouling another player seems to be a free shot at your team's goal posts. If both of these are anywhere near true, why isn't fouling the opposing Seeker a tactic that is used regularly in Quidditch? Personally, I'd start every game by clobbering the other team's Seeker.