Follow the ball’s identity at the touchline
Law 18 restricts a quick throw if a different ball is used or the original has been touched after going into touch by someone outside the specified exceptions. A convenient replacement may suit an ordinary lineout but not the quick-throw procedure.
Imagine a winger retrieving the match ball directly and preparing to throw quickly. Compare a ball attendant supplying a new ball while the original rolls away. The player is equally ready in both pictures, but the ball history differs.
The restart before the restart
Broadcast cameras often cut to players forming a lineout, missing the brief retrieval. That cut can conceal why a quick option disappeared. Watch who touched the original ball after it crossed the line and whether the ball in the thrower’s hands is actually the same one.
The explanation is about eligibility for this quick procedure, not an accusation that using a replacement ball is always improper. A normal lineout is a different restart arrangement. The useful viewing record starts at touch and ends at the proposed throw, because events during that short dead-ball interval can determine which procedure remains available.
Questions answered
Is every available ball suitable for a quick throw?
No. The same-ball requirement matters.
Does losing the quick option mean no lineout can follow?
No. The ordinary lineout is a different procedure.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.