I don't see too many people carrying DSLR with speedlight inside arena. Many people use point and shoot cameras with tiny built in flashes. My is ten times bigger and runs 4 aa batteries. It is so powerful that the people stand in front of me reflects the light to the people who stand next to me. People near me may get annoying.
Assuming both cameras and flash are allowed... (because often they're not.)
Those built-in flashes are good for about 10' -- no kidding. If someone is in the stands, they're a whole lot more than 10' away -- their flash isn't help their images at all -- they just don't know it.
Your 430EX II speedlite has a guide number of 141' feet based on an assumption of ISO 100 and (this is the biggie) f/1.0. You divide that distance by the f-stop you'll be using. If you have an f/2.8 zoom and you plan to shoot it at f/2.8 then you'd divide 141 by 2.8.
141 ÷ 2.8 = about 50'
If you have a consumer-grade zoom (e.g. f/3.5-5.6 zoom) then you'll be at f/5.6.
141 ÷ 5.6 = about 25'
That's it.
There's more... since you only get those distances if the flash can fire at full power, you CANNOT use the flash's high-speed sync mode (no HSS). That means you must keep the shutter speed at or below the camera's flash sync speed (which I think for your camera is probably 1/200th although I'm not looking it up at the moment.)
BTW, slowing the shutter speed wont make the flash carry farther, but increasing the ISO sensitivity will.
Each full stop of ISO increases the distance by a factor of 1.41. If you jump by 2 full stops you can double the distance. In other words if you shoot at ISO 400 instead of ISO 100 AND you have an f/2.8 lens then your flash will theoretically be able to get a shot 100' away. At ISO 800 you'd be back up to 141' away (at f/2.8 -- at f/5.6 you'd only be able to get a shot from 70' away.) Keep in mind these will require the full power of your flash each time it fires which can really eat through battery power. Also... depending on your metering system, the camera may meter and catch the exposure off nearby distractions (e.g. the heads of the people in front of you) and the camera will believe it doesn't need more power -- I'd be shooting with flash on manual if I were to do this.
I know a lot of events hang strings of strobes from the ceilings over the stands and these flash randomly. This is all for show... it creates the illusion from the perspective of someone watching on TV that there are lots of people in the stands with cameras taking photos. Ironically, I often see these at events where no photography is allowed.