"If a son strike his father" - shouldn't it be "strikes"?
No, it's correct. It's just old.
As @PeterShor and others comment, this is an example of the subjunctive mood, which expresses hypothetical situations and which is no longer commonly used in English. Other, more exlicit, forms of your example include:
If a son should strike his father...
Should a son strike his father...
If a son were to strike his father...