William Patrick Corgan Jr. is an American musician, songwriter, producer, poet, and professional wrestling magnate. He is best known as the lead singer, primary songwriter, guitarist, and sole permanent member of The Smashing Pumpkins. source
When we classify an issue as a 'shield issue' it is usually because we feel that someone else occupies the high ground on that issue. We feel we can't win on that issue and so we adopt a defensive posture.