College athletic trainer diagnosed me with pulled hamstring and continued to let me play college lacrosse until I tore my ACL. Is this negligence?

It is difficult to answer your question without more information.  What can be said for now is that in order for a medical malpractice action to lie, there must be a doctor-patient relationship.  Whether you could sue the trainer for malpractice based upon the possibly erroneous diagnosis would depend on whether a doctor-patient relationship existed. If you're asking whether you could sue the tainer for allowing you to play with a pulled hamstring, the answer is probably not since the decision of whether to allow a player to play with an injury usually involves the exercise of judgment, which is not usually actionable.  In addition, under the law participants in athletic activities assume the ordinary risks of the given sport. College lacrosse is a physically demanding sport with many attendant risks.  It is likely that a court would find that a torn ACL is one of those risks. This is not legal advice.  No attorney-client relationship exists at present.