If you're worried about accidentally throwing your Nintendo Switch on the ground while playing Pokémon Let's Go in public, you do not have to worry.
While an undocked version of the Let's Go titles were not available at the event, a Pokémon Company representative at the NintendoVSUK event this weekend told The OP exactly how catching Pokémon will work.
While playing the game in handheld mode, the player collides with a Pokemon in the overworld and attempted to capture it. The player must physically turn their Nintendo Switch around to find the Pokémon in a 360 degree space, but you only need to press a button to throw the Pokéball at it.
By what the Pokémon Company representative was describing, the mode seems to work like Pokémon Go's AR mode and the old 3DS eShop title, Pokémon Dream Radar combined into one capture mechanic.
Currently, Nintendo has only shown off the motion control options for The game while in docked mode, making it sound like they would be compulsory for the game. This news, however, seems to offer a different way to catch Pokémon if motion controls are not you thing.
During a trip to NintendoVSUK event in London over the weekend, Nintendo offered a surprise look at a small tech demo of Pokémon: Let's Go, Pikachu! and let's go, eevee!
Two press in attendance.
There, members of the press were able to explore Viridian Forest for a few minutes and even discovered how Shiny Pokémon will work in-game when attempting to capture it.