1. The boy is arm wrestling the girl.

2. The boy is arem wrestling with the girl.

3. The boy is having an arm wrestle with the girl.

4. The boy is having an arm wrestling against the girl.

5. The boy is doing an arm wrestle with the girl.

6. The boy is doing an arm wrestling against the girl.

(Which expressions are right and commonly used? Thank you.)

These are correct:

1. The boy is arm-wrestling the girl.

2. The boy is arm-wrestling with the girl.