This just in from Twitter
LiamTancock - "Not swimming in the 50m Backstroke tonight, looking at the bigger picture & focusing my efforts to later in the week & the rest of the year!"
Tancock went 24.52 last night in the semis to set a new textile best time. Swimmers can't qualify for the 50m Back at these trials. They need to qualify for the team on Olympic events.
By skipping the final tonight it will give Tancock a full day's rest to prepare for the 100m Free heats tomorrow and 100m Back which starts on Thursday. Scratching the final seems to show the added importance the 100m Free (and 4 x 100m Relay) has taken on for Tancock this year.