Can a person with high blood pressure play tennis?

It depends on how serious your high blood pressure is. If it is controlled with medication and you don't overdo it it shouldn't be a problem. The best advice would be to check with your doctor first.

supposedly, however; they cant work too much or they might injure themselves
I don't know why not. Having high blood pressure does not prevent you from doing the things you like to do. In fact, exercise is one of the things that the doctor likes you to do when you have high blood pressure.
Anyone with high blood pressure can be mildly active, but I would definitely check with your doctor before doing anything as strenuous as tennis or squash.

If your blood pressure is usually above 180 systolic and 110 diastolic (180/110)....you should NOT be doing any stressful activity until your blood pressure has been treated and lowered.

No game of tennis is worth a stroke.
you lowerthe BP asnd then you can lead a normal life and paly tennnis/or any other game
Yes. That's a form of exercise that will help your heart.

Here are other things to lower your H.B.P.

1) Don't smoke cigarettes or use any tobacco product.
2) Lose weight if you're overweight.
3) Exercise regularly.
4) Eat a healthy diet that includes lots of fruits and vegetables and is low in fat.
5) Limit your sodium, alcohol and caffeine intake.
6) Try relaxation techniques or biofeedback.
They should play tennis more than all the other people in the world! Exercise reduces your blood pressure and resting heart rate. Meaning: it makes your cardiovascular system work less.