give credit for EPA prior to fumble

fix_fumbles.R

#give credit for where fumble happened in EPA like how yards gained works
fix_fumbles <- function(d) {
  
  n <- d %>% filter(complete_pass == 1 & fumble_lost == 1 & !is.na(epa)) %>%
    select(desc, game_id, play_id, epa, posteam, half_seconds_remaining, yardline_100, down, ydstogo, yards_gained, goal_to_go, ep) %>%
    mutate(
      #save old stuff for testing/checking
      down_old = down, ydstogo_old = ydstogo, epa_old = epa,
      #update yard line, down, yards to go from play result
      yardline_100 = yardline_100 - yards_gained, down = ifelse(yards_gained >= ydstogo, 1, down + 1),
      #if the fumble spot would have resulted in turnover on downs, need to give other team the ball and fix
       change = ifelse(down == 5, 1, 0), down = ifelse(down == 5 , 1, down),
      #yards to go is 10 if its a first down, update otherwise
       ydstogo = ifelse(down == 1, 10, ydstogo - yards_gained), 
      #fix yards to go for goal line (eg can't have 1st & 10 inside opponent 10 yard line)
       ydstogo = ifelse(yardline_100 < ydstogo, yardline_100, ydstogo), 
      #10 yards to go if possession change
       ydstogo = ifelse(change == 1 , 10, ydstogo),
      #flip field for possession change
       yardline_100 = ifelse(change == 1, 100 - yardline_100, yardline_100),
       goal_to_go = ifelse(yardline_100 == ydstogo, 1, 0),
       ep_old = ep) %>% 
    select(-ep, -epa)
  
  t2 <- calculate_expected_points(n, "half_seconds_remaining", "yardline_100", 
                                  "down", "ydstogo", "goal_to_go") %>%
    mutate(ep = ifelse(change == 1, -ep, ep), fixed_epa = ep - ep_old) %>%
    select(game_id, play_id, fixed_epa)
  
  d <- d %>%
    left_join(t2, by=c("game_id", "play_id")) %>%
    mutate(epa = ifelse(!is.na(fixed_epa), fixed_epa, epa)) %>%
    select(-fixed_epa)
  
  return(d)
  
}