Picture-in-picture, AirPlay and the iPad as a second television
Picture-in-picture is the feature that makes an iPad genuinely useful for live television: swipe up from the player and the channel keeps playing in a corner while you use other apps. It survives switching apps and locking rotation, and it is the reason an iPad works better as a kitchen or workshop television than a phone does.
AirPlay sends the stream to an Apple TV or a compatible television, and unlike screen mirroring it hands off the actual stream rather than re-encoding the display — so the picture is cleaner and the iPad's battery lasts considerably longer. If you have both an iPad and an Apple TV, AirPlay from the iPad is a perfectly good way to watch on the big screen without touching the Apple TV's remote.
Cellular data, and how quickly live TV consumes it
Live television over cellular works and is genuinely useful when travelling, but the numbers are worth knowing in advance: roughly 2 to 3 GB per hour in HD, and more on a 4K feed. An afternoon of sport on a metered plan can consume a monthly allowance in a single sitting.
iOS gives you a per-app control at Settings, Cellular, where you can switch the app off entirely so it can never use mobile data by accident. If you would rather keep the option, use Low Data Mode on the cellular connection, which asks apps to reduce their consumption and typically drops the stream to a lower quality tier rather than cutting it off. Either is better than discovering the overage on a bill.
The iOS settings that quietly interrupt playback
Low Power Mode is the most common cause of an iPhone stream that degrades after a while. It throttles background activity and reduces the app's ability to buffer ahead, and it switches itself on automatically at 20 per cent battery — which is why the problem so often appears late in a long match rather than at the start.
Background App Refresh matters for a different reason. With it off, the guide and catch-up listings go stale and refetch when you open the app, which reads as slowness rather than as a setting. Leaving it on for this one app costs very little battery, because the refresh is a small text payload rather than video.
Auto-Lock is the third. iOS keeps the screen awake during full-screen video, but picture-in-picture is treated as background playback, so a locked phone can suspend it depending on the source. If you rely on picture-in-picture while doing something else, keep the device unlocked or use AirPlay to a television instead.