My 17 yr old son tore his ACL and wants to play football. Ss it reasonable to play with a torn acl?

Risks worse injury. Playing with a torn ACL in sports that require cutting and rapid changes of direction is not generally recommended. The intact or reconstructed ACL allows a return to such sports, but more importantly, protects against further meniscal or cartilage damage. Your son risks further irreparable damage to his meniscii and joint cartilage if he tries to play with a torn acl.
No. Playing a cutting sport with an ACL tear is not advisable...Especially if there is substantial instability. The unstable (acl-deficient) knee can lead to cartilage injuries such as meniscus tears. His knee should have acl-reconstruction in my opinion.