You’ll have to defend the case on merits. You have not given details of the offence registered against you, but it appears to be mainly under Section 354 / 323 of the IPC.
It appears that there may be two allegations against you: (i) of molestation and touching her inappropriately; (2) slapping her.
The plea of self-defence may not be available against the first act, but then you can try to prove that it was not intentional or deliberate. Self-defence plea with regard to the second allegation has to be examined as to whether it was necessary and whether it was proportional, and also whether the whole incident was caused due to your own provocation.
If other commuters in the metro, who have witnessed the said incident, are willing to support you as you have mentioned, you can enlist their support and can get them examined by police.
More than this, it may not be possible for us to help you on facts, since we cannot go into detailed facts of the case on this forum. Please consult some local lawyer by sharing with him all the necessary details.
Dr. Ashok Dhamija is a New Delhi based Supreme Court Advocate and author of law books. Read more about him by clicking here. List of his Forum Replies. List of his other articles. List of his Quora Answers. List of his YouTube Videos.