Phoenix my pig

Question
My pot-bellied pig is foaming at the mouth quite excessively, and has dug large potholes and destroyed a small tree in his pen.
His pen is quite big, about 15x15 metres, and we let him out twice a week.
It has trees, shelter, and a grass patch

He doesn't usually dig potholes though, he's dug about seven in his pen today. And the tree, he hasn't ever touched it, but its in tatters.

Rabies??
or What??

Answer
I see that you used the metric system in your question, so I am guessing you are outside the US.

Pigs often foam at the mouth. Sometimes because they smell food, or are thinking about food. Intact males foam a lot, and all the time. Pigs also foam when they are upset or angry.

If you live in a rural area, wild pigs or other animals visiting your yard at night would leave their scent and could upset your pig. Or if you're in a suburban area, your pig might be smelling a neighbors outdoor party, and frustrated he can't get the food.

Pot-bellied pigs will dig large holes to keep cool, but they usually don't destroy large areas. If something tasty was scattered on the ground, a pot-bellied pig will tear up the sod to get to the goodies. For example, if an oak tree dropped acorns all over the pen, or a squirrel hid sunflower seeds there, a pig would enjoy digging up grass looking for (and eating) the goodies. This possibility explains both the foaming and the destruction.

Intact male pigs are very energetic and restless, and could do this kind of damage. Neutering will calm him down.

Pigs are highly resistant to rabies, so that's extremely unlikely. However, there is a disease with symptoms nearly identical to rabies. But the cause is different, so the disease is called pseudorabies (fake rabies). A pig with this disease will not be restless and destructive, he will look and act sick and confused.