Because grabbing input-wise is the same as shielding and attacking at the same time, shield grabs can be done simply by pressing the attack button while shielding, instead of pressing the grab button. As a basic, simple technique, there are many ways around it, not in the least of which are cross-ups and/or shffls. However, it is still effective when used in the right situation; certain characters' grabs are so good, it is often worth the attempt, even if it fails. In competitive play, shield grabbing is most often used after shielding a high-lag attack.