Racketeering is the extortion of money under the threat of illegal violence: arson, injury, blackmail, etc. The payer has done nothing to harm the payee.

Patent trolling is the extortion of money under the threat of a legal action over a wrong done by the payer (ie, infringed on a patent).

If you hit me with your car, I can choose to sue your insurance company (you've paid them to take legal responsibility), or I can choose to accept a negotiated settlement from them.