You'll want something with good internal image stabilisation - without it, the umpire's movements will impact the footage and could ruin any chance for review, due to it being unwatchable. The other option would be to get a gimbal to keep things smooth, but that would add bulk, weight and a problem of how you'd mount it.
You'll also want to think about where you're positioning it - chest strap on the umpire may be convenient, but your umpire will need to be careful of what he's doing with his arms so as not to block the shot. A head strap could be a good option, as long as the umpire doesn't mind it. You'll probably want someone else to check on the framing of the shot from the sidelines every so often, via a connected device, so the horizon stays level etc. Also whether you can zoom may be important for decisions, either with the camera or with the software during playback.
Batteries and a big SD card are another consideration - you'll likely need at least 1 battery per innings for T20.
I assume you'd just hit record at the start of the inning and stop at the end? The other option would be to have a remote control (or have the guy with the Ipad hitting record and stop) and record every ball individually. Recording one file would be easiest, but could mean delays when reviewing - if you want to review on a device instead of the camera itself, the transfer time of a large file from the camera to a device may take longer.
I only really know about GoPros: the GoPro Hero 8 may be a good shout, as the internal image stabilisation (hypersmooth 2) is very good, it has wifi connection & has many options for mounting/wearing. The GoPro app would allow live monitoring on a device like an iphone or an ipad & you could transfer files between the two wirelessly. I think it has a basic ability to zoom in before recording, too, so you could get the framing set up nicely.