Just a brief summary of the articles I've found showing that Gareth Southgate has sought knowledge outside of his specific area:

BBC 26th June 2018 - https://www.bbc.co.uk/sport/football/44616567 - interesting that the Seahawks and the use of set-pieces are specifically mentioned.

Telegraph 26th June 2018 - https://www.telegraph.co.uk/world-cup/2018/06/26/gareth-southgate-fuelled-englands-world-cup-bid-inspiration/ - a useful summary of just how many other sports Southgate has referred to, notably the way NFL stars are presented to the media.

See also this from the Guardian https://www.theguardian.com/football/2018/jun/25/england-set-pieces-world-cup ; this from MyNorthwest in the USA http://sports.mynorthwest.com/477017/keen-to-embrace-us-sporting-ideas-southgate-revives-england/? ;

Hopefully the England team does well enough that I can use this quote from Southgate: "One of the reasons some of our guys have travelled is to see how the NFL operate because we don't have to do things the way they've always been done, we can try different things that work" ( my emphasis ) - from http://www.espn.co.uk/football/england/story/3371770/england-boss-gareth-southgate-looks-to-super-bowl-for-inspiration

And a note to myself, if I rewrite my current presentation with more soccer references, Sir Bobby Robson is very quotable: https://www.bbc.co.uk/sport/football/44605562 ; this from Alan Shearer:

As a player, I always knew there would be opportunities at set-pieces, if not for me then for one of my team-mates.

At Newcastle, Sir Bobby Robson would tell us "there is always one dope who falls asleep" and we would try to pick out the defender who would let his side down.