You can override the event handler onfocusoutin the parameters that you pass to the method .validate(). In the overridden version, some element should be processed, returning to the default, if this is not the field that you want to exclude:
$('#test').validate({
rules: {
"field1": "required",
"field2": "required",
"field3": "required"
},
onfocusout: function (element, event) {
if (element.name !== "field2") {
$.validator.defaults.onfocusout.call(this, element, event);
}
}
});
jsFiddle .