Crossword puzzle clue "lock that's hard to open"

Lock that's hard to open?

Scroll Lock or Num Lock

Force open, as a lock

Lock that doesn't open

Open, as a door lock

Rare occurrence at the U.S. Open on Father's Day that's a common occurrence at the U.S. Open on Labor Day

US Open and French Open feats

2004 French Open and U.S. Open runner-up Dementieva