4.7 Scoring vs stronger/weaker opponents

Let’s find the average points allowed for each team, and add a column to the data frame that says the average points allowed by the opp.

Code

opp.pts = dd %>%
  group_by(team) %>%
  summarise(avg.pts.allowed = mean(opp.score))

dd = dd %>% 
  left_join(opp.pts, 
            by = c('opp' = 'team'))
head(dd)

        date team score opp opp.score season      gid   ha avg.pts.allowed
1 2020-12-22  GSW    99 BKN       125   2021 22000001 away        113.0325
2 2020-12-22  BKN   125 GSW        99   2021 22000001 home        108.8247
3 2020-12-22  LAC   116 LAL       109   2021 22000002 away        111.2208
4 2020-12-22  LAL   109 LAC       116   2021 22000002 home        108.1299
5 2020-12-23  MIL   121 BOS       122   2021 22000003 away        107.6039
6 2020-12-23  BOS   122 MIL       121   2021 22000003 home        113.1169

Code

tms = read.csv('data/nba.teams.csv')

tms = tms %>% 
  arrange(conf, div) %>%
  mutate(conf = paste0(toupper(substr(conf, 1, 1)), substr(conf, 2, nchar(conf))),
         div  = paste0(toupper(substr(div , 1, 1)), substr( div, 2, nchar( div))), 
         div  = factor(div, levels = unique(div)))
head(tms)

dg = dd %>%
  left_join(tms %>% select(-conf), 
            by = 'team') %>%
  group_by(div) %>%
  mutate(group = 
           team %>% 
           as.factor() %>% 
           as.numeric() %>% 
           as.character())

head(dg)

  team      div conf
1  BKN Atlantic East
2  BOS Atlantic East
3  NYK Atlantic East
4  PHI Atlantic East
5  TOR Atlantic East
6  CHI  Central East
# A tibble: 6 × 11
# Groups:   div [3]
  date       team  score opp   opp.score season gid      ha    avg.pts.allowed
  <date>     <chr> <dbl> <chr>     <dbl> <chr>  <chr>    <chr>           <dbl>
1 2020-12-22 GSW      99 BKN         125 2021   22000001 away             113.
2 2020-12-22 BKN     125 GSW          99 2021   22000001 home             109.
3 2020-12-22 LAC     116 LAL         109 2021   22000002 away             111.
4 2020-12-22 LAL     109 LAC         116 2021   22000002 home             108.
5 2020-12-23 MIL     121 BOS         122 2021   22000003 away             108.
6 2020-12-23 BOS     122 MIL         121 2021   22000003 home             113.
# ℹ 2 more variables: div <fct>, group <chr>

Code

title = "Points Scored vs Average Opp Points Allowed" 

g = ggplot(dg, aes(x     = avg.pts.allowed, 
                   y     = score, 
                   group = group, 
                   color = group))+
  geom_jitter(width  = 0.1, 
              height = 0.1, 
              alpha  = 0.1, 
              size   = .75, 
              show.legend = F) +
  geom_smooth(method = 'lm', 
              alpha  = 0.1, 
              se     = F, 
              size   = 1,
              show.legend = F) +
  geom_abline(slope = 1, 
              intercept = 0) + 
  facet_wrap(~div, 
             nrow = 2) +
  labs(title = title,
       x     = 'Avg Points Allowed by Opponent',
       y     = 'Points Scored in the Game')

g %>% 
  pub(xlim  = c(105, 119), 
      ylim  = c(80 , 150), 
      facet = T)

[1] 57.35768
[1] 80
[1] 20
[1] 157.3577