Table 3

Player behaviour features and diagnostic performance characteristics following helmet strike between the HS-C and HS-NC groups

Player behaviour feature	Frequency HS-C N=16	Frequency HS-NC N=153	χ² with p values	Sensitivity (%)	Specificity (%)
Player follows ball after strike	5	63	0.63 p-0.59	31.25	58.56
Player removes or checks helmet	12	56	13.01 p-<0.001	92.31	59.71
Other players—relaxed	7	57	0.34 p-0.58	50	58.09
Other players—concerned	0	11	1.21 p-0.6	0	91.97
Other players—urgent	5	11	10.28 p-0.01	35.71	91.97
Player stumbles	4	32	0.11 p-0.75	33.33	78.67
Player falls to knees	2	12	0.40 p-0.63	12.5	92.11
Player falls over	3	7	5.23 p-0.06	18.75	95.42
Player stumbles getting back to feet	0	2	0.20 p-1.0	0	98.62
Walks away from play	4	64	0.53 p-0.56	33.33	55.86
Player holds face/head	4	19	2.71 p-0.11	30.77	86.33
Player bends head down	7	36	3.73 p-0.07	50	94.55
Player immediately alert	4	67	2.63 p-0.12	25	53.79
Play resumes immediately	1	56	6.48 p-0.01	6.67	60
Player appears dazed	5	16	5.05 p-0.04	50	81.18
More than 4 s to resume	11	61	8.13 p-0.01	91.67	51.59
Player knocked backwards	3	43	0.66 p-0.56	18.75	71.71