A counter claim, even if filed after the written statement is filed, can be entertained as a regular plaint or a cross suit, subject to satisfaction of all the rules that are applicable to the institution of a regular suit.
Sugesan and Co. Pvt. Ltd. vs. Hindustan Machine Tools Ltd., AIR 2004 AP 428 (para 38)
A right to file counter claim is an additional right and it may be filed in respect of any right or claim the cause of action so however must accrue either before or after the filing of suit but before the defendant has raised his defence. [Order VIII Rule 6A]
Bollepanda P. Poonacha and Anr. vs. K.M. Madapa, AIR 2008 SC 2003
Counter-claim or set-off must be pleaded by way of defence in the written statement before the defendant filed his written statement or before the time limit for delivering the written statement has expired, whether such counter claim is in the nature of a claim for damages or not.